Haramaya University: College of Business and Economics
Haramaya University: College of Business and Economics
                               November 12/2021
                               Haramaya university
1. Write short notes on steps on Decision Modelling
Solution
1. Formulation
       Translating a problem scenario from words to a mathematical model
2. Solution
       Solving the model to obtain the optimal solution
3. Interpretation and Sensitivity Analysis
       Analyzing results and implementing a solution
2, Discuss Assumptions of Linear Programming problem
Solution;
    1. 1 Proportionality. - The contribution of each decision variable to the objective or
       constraint is directly proportional to the value of the decision variable.
    2. Additivity. - The contribution to the objective function or constraint for any variable is
       independent of the values of the other decision variables, and the terms can be added
       together sensibly.
    3. Divisibility. - The decision variables are continuous and thus can take on fractional
       values.
    4. Deterministic. - All the parameters (objective function coefficients, right-hand side
       coefficients, left-hand side, or technology, coefficients) are known with certainty.
3. Find solution using Simplex method
MAX Z = 5x1 + 7x2
subject to
x1 <= 6
2x1 + 3x2 <= 19
x1 + x2 <= 8
and x1,x2 >= 0
Solution: Problem is
The problem is converted to canonical form by adding slack, surplus and artificial variables as
appropiate
1. As the constraint-1 is of type '≤' we should add slack variable S1
2. As the constraint-2 is of type '≤' we should add slack variable S2
3. As the constraint-3 is of type '≤' we should add slack variable S3
After introducing slack variables
Max Z
          x     x     S      S  S
=         5+ 7 + 0 + 0 + 0
          1     2     1      2  3
subject to
  x1        + S1           =6
 2x1 + 3 x2      + S2      = 19
  x1 + x2             + S3 = 8
and x1,x2,S1,S2,S3≥0
       Iteration-1                            Cj                  5            7       0    0    0
                                                                                                        MinRatio
             B                CB              XB                  x1        x2         S1 S2 S3
                                                                                                         XBx2
S1 0 6 1 0 1 0 0 ---
S2 0 19 2 (3) 0 1 0 193=6.3333→
S3 0 8 1 1 0 0 1 81=8
Z=0 Zj 0 0 0 0 0
                                             Zj-Cj                -5       -7↑         0    0    0
Negative minimum Zj-Cj is -7 and its column index is 2. So, the entering variable is x2.
Minimum ratio is 6.3333 and its row index is 2. So, the leaving basis variable is S2.
∴ The pivot element is 3.
Entering =x2, Departing =S2, Key Element =3
R2(new)=R2(old)÷3
R1(new)=R1(old)
R3(new)=R3(old) - R2(new)
Iteration-2 Cj 5 7 0 0 0
B CB XB x1 x2 S1 S2 S3 MinRatio
S1 0 6 1 0 1 0 0 61=6
    Iteration-3                    Cj          5          7            0           0        0
          B            CB      XB       x1     x2        S1   S2   S3   MinRatio
S1 0 1 0 0 1 1 -3
x2 7 3 0 1 0 1 -2
x1 5 5 1 0 0 -1 3
Z=46 Zj 5 7 0 2 1
                              Zj-Cj      0      0        0    2    1
Since all Zj-Cj≥0
Hence, optimal solution is arrived with value of variables as :
x1=5,x2=3
Max Z=46
B. Find solution using graphical method
MAX Z = 5x1 + 7x2
subject to
x1 <= 6
2x1 + 3x2 <= 19
x1 + x2 <= 8
and x1,x2 >= 0
Solution: Problem is
Max zx
           x     x
=         5+ 7
           1     2
subject to
  x1        ≤6
 2x1 + 3 x2 ≤ 19
  x1 + x2 ≤ 8
and x1,x2≥0;
1. To draw constraint x1≤6→(1),        x1=6
Here line is parallel to Y-axis, X1= (6,6), X2= (0, 1)
2. To draw constraint 2x1+3x2≤19→(2)
The value of the objective function at each of these extreme points is as follows:
  Extreme Point
                                                                   Objective function value
   Coordinates            Lines through Extreme Point
                                                                          Z=5x1+7x2
      (x1,x2)
       O(0,0)                        4→x1≥0                               5(0)+7(0)=0
                                     5→x2≥0
                                     1→x1≤6
      A(6,0)                                                            5(6)+7(0)=30
                                     5→x2≥0
                                     1→x1≤6
      B(6,2)                                                            5(6)+7(2)=44
                                    3→x1+x2≤8
                                   2→2x1+3x2≤19
      C(5,3)                                                            5(5)+7(3)=46
                                    3→x1+x2≤8
                                   2→2x1+3x2≤19
     D(0,6.33)                                                        5(0)+7(6.33)=44.33
                                     4→x1≥0
         x   x       x
=        5+ 2 +
         1   2       3
subject to
  x1 + 3 x2 - x3 ≤ 6
         x2 + x3 ≤ 4
 3x1 + x2        ≤7
and x1,x2,x3≥0;
The problem is converted to canonical form by adding slack, surplus and artificial
variables as appropriate
The problem is converted to canonical form by adding slack, surplus and artificial variables as
appropiate
1. As the constraint-1 is of type '≤' we should add slack variable S1
2. As the constraint-2 is of type '≤' we should add slack variable S2
3. As the constraint-3 is of type '≤' we should add slack variable S3
After introducing slack variables
Max Z
          x     x      x   S      S S
=         5+ 2 +       + 0 + 0 + 0
          1     2      3 1        2 3
subject to
  x1 + 3 x2 - x3 + S1           =6
         x2 + x3      + S2      =4
 3x1 + x2                  + S3 = 7
and x1,x2,x3,S1,S2,S3≥0
Iteration-1 Cj 5 2 1 0 0 0
B CB x1 x2 x3 S1 S2 S3 RHS Ratio
0 S1 1 3 -1 1 0 0 6 ----
0 S2 0 1 1 0 1 0 4 -----
0 S3 3 1 0 0 0 1 7 -----
Z=0 Zj 0 0 0 0 0 0
Cj-Zj 5 2 1 0 0 0
Posive Maximum CJ ZJ = 11.25-1.5M and its column index is 2 so the intering variable is x2
The minmum ratio is 3.33
The pivot element is 1.5
Iteration 3
       CJ
       BV        X1 X2 S1        S2       RHS
25 X1            1     0 -0.1 0.5         25
30 X2            0     1 0.66 -0.667 30
                         7
       ZJ        25 30 -0.5 -7.5
       CJ-ZJ 0         0 -0.5 -7.5
Since all cj - zj <= 0
Hence optimal solution is arrived with value of variable as x1= 2.5, x2 = 3.33
         MIN Z = 162.5
C. Find simlex exell method
 min                    x1         x2                        
 decision variable           2.5    3.333333   162.5         
 objective                   25           30   162.5 LHS    RHS
 constrain1                  20           15            100    100
 constraint 2                  2           3             15     15
6.    A firm makes two types of furniture chairs and tables. The contribution for each product to
objective function is birr 20 per chair and birr 30 per table respectively. Both products are
processed on three Machines M1, M2 and M3. The time required (in hours) by each product and
total time available per week on each machine are as follows:
         Machine               Chair              Table                Available time
         M1                    3                  3                    36
         M2                    5                  2                    50
         M3                    2                  6                    60
How should the manufacturer schedule his production in order to maximize contribution?
Solution
✓ For M1= Total Possible in one week
       36 ÷ 3 = 12
Total table possible in one week
36 ÷ 3 = 12
Total Profit per week
12 × 20 +12 × 30 = 600
✓ For M2
Total chairs possible in one week
50 ÷ 5 = 10
Total table possible in one week
50 ÷ 2 = 25
Total Profit per week
10 × 20 + 25 × 30 = 950
✓ For M3
Total chair possible in one week
     60 ÷ 2 = 30
Total table possible in one week
60 ÷ 2 = 30
Total table possible in one week
60 ÷ 6 = 10
Total profit per week
30 × 20 + 10 × 30 = 900
Their fore manufacture used M2 for maximized contribution
7.       Consider the transportation problem having the following parameter table:
                                                Destination                           Supply
                                                1                    2
  Source            1                           8                    5                4
                    2                           6                    4                2
Demand                                          3                    4
North-West Corner (NWC) Method, Least Cost Method (LCM), and Vogels Approximation (or
penalty) Method (VAM, obtain the initial basic feasible solution and show the corresponding
total transportation cost.
Solution North-West Corner (NWC) Method,
Step 1
                                            Destination
                        D1                          D2                   Supply
S1                          8         (3)           5      (1)           4   1    0
S2                      6                           4                    2
Ddummy                  0                           0                    1
Demand 3 0 4 3
TC = 8 × 3 + 5 ×1 + 4 × 2 + 0 ×1                =   37
Find the least Cost Method
                        D1                          D2                   Supply
S1                      8       (2)                 5     (2)            4
S2                  6                    4    (2)            2
Ddummy              0 (1)                0                   1
Demand              3                    4
D1 D2 D3 Supply
S1 8 5 6 120
S2 15 10 12 80
S3 3 9 10 80
Demand 140 80 50
                                 D1              D2               D3              Supply
              S1                    8               5            6             120
S2 15 10 12 80
S3 3 9 10 80
Demand 140 80 50
Here Total Demand = 270 is less than Total Supply = 280. So We add a dummy demand
constraint with 0 unit cost and with allocation 10.
Now, The modified table is
D1 D2 D3 Ddummy Supply
S1 8 5 6 0 120
S2 15 10 12 0 80
S3 3 9 10 0 80
Demand 140 80 50 10
D1 D2 D3 Ddummy Supply
S1 8(120) 5 6 0 0
S2 15 10 12 0 80
S3 3 9 10 0 80
Demand 20 80 50 10
D1 D2 D3 Ddummy Supply
S1 8(120) 5 6 0 0
S2 15(20) 10 12 0 60
S3 3 9 10 0 80
Demand 0 80 50 10
D1 D2 D3 Ddummy Supply
S1 8(120) 5 6 0 0
S2 15(20) 10(60) 12 0 0
S3 3 9 10 0 80
Demand 0 20 50 10
D1 D2 D3 Ddummy Supply
S1 8(120) 5 6 0 0
S2 15(20) 10(60) 12 0 0
               S3           3          9(20)          10               0               60
             Demand             0                0                50             10
D1 D2 D3 Ddummy Supply
S1 8(120) 5 6 0 0
S2 15(20) 10(60) 12 0 0
S3 3 9(20) 10(50) 0 10
Demand 0 0 0 10
D1 D2 D3 Ddummy Supply
S1 8(120) 5 6 0 0
S2 15(20) 10(60) 12 0 0
Demand 0 0 0 0
D1 D2 D3 Ddummy Supply
S1 8 (120) 5 6 0 120
S2 15 (20) 10 (60) 12 0 80
D1 D2 D3 Supply
S1 8 5 6 120
S2 15 10 12 80
S3 3 9 10 80
Demand 140 80 50
D1 D2 D3 Supply
S1 8 5 6 120
S2 15 10 12 80
S3 3 9 10 80
Demand 140 80 50
Here Total Demand = 270 is less than Total Supply = 280. So We add a dummy demand
constraint with 0 unit cost and with    allocation 10.
      Now, The modified table is
D1 D2 D3 Ddummy Supply
S1 8 5 6 0 120
S2 15 10 12 0 80
             S3                3               9              10            0             80
               Demand           140            80             50            10
D1 D2 D3 Ddummy Supply
S1 8 5 6 0(10) 110
S2 15 10 12 0 80
S3 3 9 10 0 80
Demand 140 80 50 0
D1 D2 D3 Ddummy Supply
S1 8 5 6 0(10) 110
S2 15 10 12 0 80
S3 3(80) 9 10 0 0
Demand 60 80 50 0
                        D1     D2             D3                   Ddummy            Supply
            S1         8       5(80)            6                   0(10)                30
S2 15 10 12 0 80
S3 3(80) 9 10 0 0
Demand 60 0 50 0
D1 D2 D3 Ddummy Supply
S2 15 10 12 0 80
S3 3(80) 9 10 0 0
Demand 60 0 20 0
D1 D2 D3 Ddummy Supply
S2 15 10 12(20) 0 60
S3 3(80) 9 10 0 0
Demand 60 0 0 0
D1 D2 D3 Ddummy Supply
S2 15(60) 10 12(20) 0 0
S3 3(80) 9 10 0 0
Demand 0 0 0 0
D1 D2 D3 Ddummy Supply
S2 15 (60) 10 12 (20) 0 80
S3 3 (80) 9 10 0 80
Demand 140 80 50 10
D1 D2 D3 Supply
S1 8 5 6 120
S2 15 10 12 80
S3 3 9 10 80
Demand 140 80 50
S1 8 5 6 120
S2 15 10 12 80
S3 3 9 10 80
Demand 140 80 50
Here Total Demand = 270 is less than Total Supply = 280. So We add a dummy demand
constraint with 0 unit cost and with         allocation 10.
Now, The modified table is
D1 D2 D3 Ddummy Supply
S1 8 5 6 0 120
S2 15 10 12 0 80
S3 3 9 10 0 80
Demand 140 80 50 10
Table-1
S1 8 5 6 0 120 5=5-0
S2 15 10 12 0 80 10=10-0
S3 3 9 10 0 80 3=3-0
Demand 140 80 50 10
S1 8 5 6 0 120 1=6-5
S2 15 10 12 0(10) 70 2=12-10
S3 3 9 10 0 80 6=9-3
Demand 140 80 50 0
S1 8 5 6 0 120 1=6-5
S2 15 10 12 0(10) 70 2=12-10
S3 3(80) 9 10 0 0 --
Demand 60 80 50 0
S1 8(60) 5 6 0 60 1=6-5
S2 15 10 12 0(10) 70 2=12-10
S3 3(80) 9 10 0 0 --
Demand 0 80 50 0
S1 8(60) 5 6(50) 0 10 5
S2 15 10 12 0(10) 70 10
S3 3(80) 9 10 0 0 --
Demand 0 80 0 0
ClmnPenalty -- 5=10-5 -- --
S1 8(60) 5 6(50) 0 10 5
S2 15 10(70) 12 0(10) 0 --
S3 3(80) 9 10 0 0 --
Demand 0 10 0 0
CmnPnlty -- 5 -- --
      S2           15            10(70)       12           0(10)           80         10 | 2 | 2 | 2 | 10 | --
                                                                                                   |
S3 3(80) 9 10 0 80 3 | 6 | -- | -- | -- | -- |
Demand 140 80 50 10
   Column           5              4          4             0
   Penalty          5              4          4             --
                    7              5          6             --
                    --             5          6             --
                     --            5        --         --
                     --            5        --         --
             1                                          50
                   2                                              150
                   3                                              300
     The manager of the sand and gravel pit has estimated the cost per cubic yard to ship over each of
     the possible routes:
           From/to          Cost per cubic yard to
                            Project #1          Project #2        Project #3
           Farm A           Birr 4              Birr 2            Birr 8
           Farm B               5                1                 9
           Farm C               7                6                 3
            Solution
     A. arrange the information into a transportation table
From/to                             Cost per cubic yard to
                       Project #1      Project #2        Project #3        Wkly cpcity (cubic yards)
Farm B 5 1 9 200
Farm C 7 6 3 200
     B. Write the above transportation problem in the form of linear programming problem.
     Min z = 4x11 + 2x12 +8x13 + 5x21 + 1x22 + 9x23 + 7x31 + 6x32 + 3x33
     Subject to:
     Weekly Capacity Constraint: 4x11 + 2x12 + 2x13 >= 100
                                      5x22 + 1x22 + 9x23 >= 200
                                      7x31 + 6x32 + 3x33 >= 200
     Weekly demand Constraint:          4x11 + 5x21 + 7x31 >= 50
                                         2x12 + 1x22 + 6x32 >= 150
                                  8x13 + 9x23 + 3x33 >= 300
     C. Find the feasible solution using North-West Corner (NWC) Method, Least Cost Method
   (LCM), and Vogels Approximation (or penalty) Method (VAM).
 North-West Corner (NWC) Method
   Find Solution using North-West Corner method
                  Pro1    pro2   pro3   Supply
   S1.               4    2      8      100
   S2             5       1      9      200
   S3                7    6      3      200
   Demand            50   150    300
   Solution:
   TOTAL number of supply constraints : 3
   TOTAL number of demand constraints : 3
   Problem Table is
                 Proj1    proj2 pro3          Supply
   S1            4        2      8            100
   S2             5       1      9            200
   S3             7       6      3            200
   Demand            50   150    300
   Problem is Maximization, so convert it to minimization by subtracting all the elements from max
   element (9)
                 D1       D2     D3              Supply
   S1             5       7      1               100
   S2             4       8      0               200
   S3             2       3      6               200
   Demand        50       150    300
Table-2
            Proj1     2              D3               Supply
S1         5(50)      7(50)           1               0
S2            4        8              0               200
S3            2        3              6               200
Demand        0       100            300
  Farm A                        4                2              8             100
  Farm B                        5                1              9             200
  Farm C                        7                6              3             200
  W/ demand(cubic yards         50               150            300
Farm A 2 2 8 100
Farm B                         5                   1                  9            200
Farm C                         7                   6                  3            200
10. A manager has prepared a table that shows the cost of performing each of four jobs by each
of four employees. According to this           Table, Job 1 will cost $15 if done by Employee A, $20 if
it is done by Employee B, and so on. The manager has stated that his goal is to develop a set of
job assignments that will minimize the total cost of getting all four jobs done. It is further
required that the jobs Be performed simultaneously, thus requiring one job being assigned to
each employee. Although the manager recognizes that this Problem can be solved using the
simplex routine; he also knows that he can solve the problem by hand using the assignment
method.
    Job Costs for Each Possible Pairing
            Employees
                 A         B      C        D
            1    $15       20     18       24
            2    12        17     16       15
    Job     3    14        15     19       17
            4    11        14     12       13
          Required:
A. Formulate a linear Programming problem
B. Which salesperson should be assigned to each region to minimize total time? Identify the
optimal assignments and compute total minimum time. Use the Hungarian Method
Solution
                      A            B              C              D                Supply
1                     15           20             18             24               1
2                     12           17             16             15               1
3                     14           15             19             17               1
4                     11           14             12             13               1
Demand                1            1              1              1
Min C = 15 X11 + 20X12 + 18X13 + 24X14 + 12X21 + 17X22 + 16X23 + 15X24 + 14X31 +
15X32 + 19X33 + 17X34 + 11X41 + 14X42 + 12X43 + 13X44
Subject to;
Supply constraint; X11 + x12 + x13 + x14 >= 1
                           X21 + x22 + x23 + x24 = 1
                           X31 + X32 + X33 + X34 = 1
                           X41 + X42 + X43 + X44 = 1
Demand constraint; X11+ X21 + X31 + X44 = 1
B Find Solution of Assignment problem using Hungarian method
Work\Job        1              2                3               4
A               15             12               14              11
B               20             17               15              14
C               18             16               19              12
D               24             15               17              13
                    1          2            3              4         Row Mini
       A         4             1            3              0           (-11)
       B         6             3            1              0           (-14)
       C         6             4            7              0           (-12)
       D        11             2            4              0           (-13)
Step-2: Find out the each column minimum element and subtract it from that column.
                         1             2               3                    4
       A                 0            0                2                    0
       B                 2            2                0                    0
       C                 2            3                6                    0
       D                 7            1                3                    0
 Colm min               (-4)         (-1)             (-1)             (-0)
Iteration-1 of steps 3 to 6
Step-3: Make assignment in the opporunity cost table
Step-3: Make assignment in the opporunity cost table
(1) Rowwise cell (C,4) is assigned, so columnwise cell (A,4),(B,4),(D,4) crossed off.
(3) Columnwise cell (A,1) is assigned, so rowwise cell (A,2) crossed off.
Rowwise&columnwise assignment shown in table
                       1       2                    3                     4
        A             [0]      0                 2                       0
        B             2        2                [0]                      0
        C             2        3                 6                       [0]
        D             7        1                 3                       0
Step-5: Draw a set of horizontal and vertical lines to cover all the 0
Step-5: Cover the 0 with minimum number of lines
(1) Mark(✓) row D since it has no assignment
(4) Since no other rows or columns can be marked, therefore draw straight lines through the
unmarked rows A,B and marked columns 4
                 1              2               3              4
    A           [0]             0               2              0
B 2 2 [0] 0
    C            2              3               6             [0]         ✓(3)
    D            7              1               3              0          ✓(1)
                                                              ✓
                                                              (2)
Iteration-2 of steps 3 to 6
Step-3: Make assignment in the opporunity cost table
(2) Rowwise cell (C,4) is assigned, so columnwise cell (D,4) crossed off.
(3) Rowwise cell (D,2) is assigned, so columnwise cell (A,2) crossed off.
                    1                  2               3                4
    A              [0]                 0               2               1
    B               2                  2              [0]              1
    C               1                  2               5               [0]
    D               6                 [0]              2               0
Step-4: Number of assignments = 4, number of rows = 4
Which is equal, so solution is optimal
Optimal assignments are
                              1                  2                3              4
        A                    [0]                0                2              1
        B                    2                  2                [0]            1
        C                    1                  2                5              [0]
        D                    6                  [0]              2              0
Optimal solution is
           Tc     15+ 15 + 12 + 15 = 57
11. A firm makes air coolers of three types and markets these under the brand name
Symphony.
The relevant details are as follows:-
                    Product A (hrs. /     Product B (hrs. /   Product C (hrs,/   Total hrs.
                    unit)                unit)                unit)              available
Designing           0                    10                   20                 320
Manufacturing       60                   90                   120                1600
Painting            30                   40                   60                 1120
Profit              $300                 $700                 $900
Required:
Formulate a linear Programming problem
What Quantity of each product must be made to maximize the total profit of the firm? Use
simple procedure.
Solution
Formulate linear programing problem
Max z =300x1 + 700x2 + 900x3
  Subject to:
Designing :         10x2 + 20X3 <= 320
Manufacturing :       60x1 + 90x2 + 120x3 <= 1600
Painting:.            30x1 + 40x2 + 60x3 <= 1120
What Qty. of each product must be made to maximize the total profit of the firm?
Let X1, X2, X3 denote the Qty. of each product made
Then: Maximize: 300 X1+ 700 X2 +900 X3
Subject to:
0 X1 +10 X2 + 20 X3 ≤ 320
60 X1 +90 X2 + 120 X3 ≤ 1600
30 X1 +40 X2 + 60 X3 ≤ 1120
Introducing slacks:
Maximize Z = 300X1 +700X2 + 900X3 +0S1+ 0S2+ 0S3
Subject to: 0X1 +10X2 + 20X3 +S1+ 0S2+ 0S3 =320
              60X1 +90X2 + 120X3 +0S1+ S2+ 0S3 =1600
             30X1 +40X2 + 60X3 +0S1+ 0S2+ S3 =11
              X1, X2, X3, S1, S2, S3 >= 0
12.   The Omega pharmaceutical firm has five salespersons, which the firm wants to assign to
five sales regions. Given their various previous contacts, the salespersons are able to cover the
regions in different amounts of time. The amount of time (days) required by each salesperson to
cover each city is shown in the following table.
Requerd;
Formulate a linear Programming problem
Which salesperson should be assigned to each region to minimize total time? Identify the optimal
assignments and compute total minimum time. Use the Hungarian Method
Solution: a.
b. Step 1
                               Region
Sales person      A             B              C              D              E
1                 6             1              6              7              9
2                 1             0              7              0              3
3                 0             7              5              6              1
4                 3             1              1              9              6
5                   2         3              0                   6           0
b. Which salesperson should be assigned to each region to minimize total time? Identify the
optimal assignments and compute total minimum time. Use the Hungarian Method
Answer Row reduction:
                    A             B              C                   D                   E
1                   7             0              5                   6                   10
2                   3             0              7                   0                   5
3                   0             5              3                   4                   1
4                   4             0              0                   8                   7
5                   4             3              0                   6                   2
Column reduction:
A               B                     C                  D                       E
7               0                     5                  6                       9
3               0                     7                  0                       4
0               5                     3                  4                       0
4               0                     0                  8                       6
4               3                     0                  6                       1
A B C D E
7              0                  5                  6                   9
3              0                  7                  0                   4
0              5                  3                  4                   0
4              0                  0                  8                   6
4              3                  0                  6                   1
Final step is as follows:
A                       B              C                     D                       E
6                       0              5                     5                       4
3                       1              8                     0                       8
0                6   4   4   0
4                0   0   7   5
3                3   0   5   0
B→1
C→4
A→3
D→2
E→5
Total= 51 days