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Ex1-CO3 TALAG

This document contains solutions to 5 problems: 1) Finding the additive inverse of 6 mod 10 (which is 4) and the multiplicative inverse of 5 mod 11 (which is 9). 2) Converting time values between a 12 hour and 24 hour clock. For example, 55 hours after 7am is 2pm. 3) Determining the day of the week 125 days in the future. If today is Tuesday, Labor Day will be on Monday. 4) Checking the validity of an ISBN number by summing the digits with weights and seeing if the result is divisible by 10. The given number is invalid but can be fixed by changing the last digit to a 7. 5)

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386 views4 pages

Ex1-CO3 TALAG

This document contains solutions to 5 problems: 1) Finding the additive inverse of 6 mod 10 (which is 4) and the multiplicative inverse of 5 mod 11 (which is 9). 2) Converting time values between a 12 hour and 24 hour clock. For example, 55 hours after 7am is 2pm. 3) Determining the day of the week 125 days in the future. If today is Tuesday, Labor Day will be on Monday. 4) Checking the validity of an ISBN number by summing the digits with weights and seeing if the result is divisible by 10. The given number is invalid but can be fixed by changing the last digit to a 7. 5)

Uploaded by

rohs apacer
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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Download as PDF, TXT or read online on Scribd
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A1-CO4

1. determine the value of the following:

a. Additive inverse of 6 mod 10

- 6+x=10

-x=10-6

-x=4

b. Multiplicative inverse of 5 mod 11

- 9≡5

−1

(mod11)⇔9×5≡1(mod11)
- x=9

2. In a 12 hour clock determine the time

a. 55 hours after 7 o’clock

After 12 hours it will be 7 o’ clock

After 24 hours it will be 7 o’clock

After 48 hours it will be 7 o’clock

55hours - 48 hours = 7 hours

7 oclock + 7 hours = 2 o’clock

b. 25 hours before 2 o’clock

Before 12 hours it will be 2 o’clock

Before 24 house will be 2 o’clock

25 hours - 24 hours = 1 hour

2 oclock - 1 hour = 1 o’clock

3. In exactly 125 days the day will commemorate Labor day (may 1). If today is
tuesday, what day of the week is labor day.

125/7 = 17 weeks + 6 days

If labor day is after 125 days then if today is tuesday then the labor day it will be
monday.

4. Determine whether the given isbn code 978-971-98-0456-6 is valid or not. If the
code is not valid, give the correct check digit.
(9*1)+(7*3)+(8*1)+(9*3)+(7*1)+(1*3)+(9*1)+(8*3)+(0*1)+(4*3)+(5*1)+(6*3)+(
6*1) = 149

This ISBN code is not valid because the sum is not divisible by 10. Let's change
the last number by 7

(9*1)+(7*3)+(8*1)+(9*3)+(7*1)+(1*3)+(9*1)+(8*3)+(0*1)+(4*3)+(5*1)+(6*3)+(
7*1) = 150

This new ISBN code is valid because the sum is divisible by 10 so the new ISBN
code is 978-971-98-0456-7

5. Determine whether the credit card number 3-8137-115208-7 is valid or not.

0 1 2 3 4 5 6 7 8 9 10 11
3 8 1 3 7 1 1 5 2 0 8 7

Take all the digits in the odd place from right to left then add those numbers

7 + 0 + 5 + 1 + 3 + 8 = 24

Then take all the numbers in the even places including the number in the
zeroth place from right to left. After that multiply each digit by two and if
that digit got a product with 2 digits add those numbers. For example 9 then
multiply it by 2 you get 18 then 18 is a two digit number then add 1 + 8 it
will be 9.

(8*2) + (2*2) + (1*2) + (7*2) + (1*2) + (3*2)

= 16 + 4 + 2 + 14 + 2 + 6

= 1+6+4+2+1+4+2+6
= 26

Then add the sum of digit in the odd and in the even place

26+24 = 50

Note: if the sum of digits in the odd and in the even place are in divisible by
10 then the credit card number is valid

So the sum of the digits in the odd and even place is 50 and 50 is divisible
by 10 then the credit card number is valid.

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