Probability

Working with independent events


When two events are independent then to calculate the probability of both events occurring we just multiply together the individual probabilities of each event.

So, if 75% of cats in a town are black and the probability that a black cat is friendly is 80% then what's the probability of bumping into a friendly black cat in a dark alleyway?

Well, the probability of meeting a black cat is 75% and the probability that the black cat is friendly is 80%. So, to calculate the probability of meeting a friendly black cat we just multiply together these two probabilities, so ...

                                               Probability = 75% x 80%

                                                                       = 60%


Let's try another example ...



The probability that Bob can beat Bert at tennis is 60%.

The probability that Bob can beat Bert at both tennis and bowling is 25%

What is the probability that Bob will beat Bert at bowling?


Well, if we call the probability that Bob will beat Bert at bowling 'p' then ...



So, if we adjust the equation to solve for 'p' then ...

                                               p = 25% / 60%
               So,
                                               p = 41.6667%

So, the probability that Bob will beat Bert at bowling is 41.6667%!