Probability
Probability – a measure of how likely a particular event Inclusive events
will occur. We denote the probability of an event E Two events, A and B, are events from a sample
occurring as P(E). It can take on any value between 0 space S. The probability that either A or B will occur,
and 1 inclusive. denoted by is:
Experiment – involves performing a number of trials to
enable us to measure the chance of an event occurring Independent Events
in the future. If the occurrence or nonoccurrence of event A
does not affect the occurrence or nonoccurrence of
Sample Space – the set S whose elements are all event B, then A and B are independent events.
possible outcomes of an experiment.
Event – set of outcomes that are a subset of the sample
space. Conditional Probability
Let A and B be two events in S, such that P(A) is
non-zero. If event A is a condition for event B, then
where: P(E) – probability of an event to happen
S – sample space
E – event Multiplication Rule
n(S) – cardinality of the sample space If in an experiment the events A and B can both
n(E) – cardinality of the event occur then,
Events
Complementary Events
Given the event E in a sample space S, the
complement of E, denoted by EC, consists of all Exercises:
1. A card is drawn from a well-shuffled deck of 52
outcomes in S but not in E. cards. What is the probability of drawing a card
with a number printed on it that is less than
four?
2. A block is chosen at random from a bag
containing 6 white blocks, 4 purple blocks and
If the probability that an event occurs is p (where p
12 red blocks. What is the probability that it
≠ 0 and p ≠ 1), then will be a red or a white block?
3. A tire manufacturer found that 10% of the tires
Odds in favor of the event = p : (1 – p) produced had cosmetic defects and 2% had
Odds against the event = (1 – p) : p both cosmetic and structural defect. What is
the probability that one tire selected at random
is structurally defective if it is known that it has
Mutually Exclusive Events a cosmetic defect?
Two events, A and B are mutually exclusive if 4. Imagine two women, each of whom tells the
and only if they have no outcomes in common. truth only two-thirds of the time. If both say
that it is raining, what is the probability that it
Therefore, they cannot occur at the same time. is really raining?