Question

In a restaurant, if a customer orders a starter, then the probability that they

order a dessert is
If a customer does not order a starter, then the probability that they order a
dessert ist
What fractions should go in the boxes marked A and B on the tree diagram?

Answer 1

Explanation:

since in both cases there are always only 2 possible outcomes, the 2 probabilities together must always be 1.

so, if they had a starter then the probability of not ordering dessert is 1 - 1/5 = 4/5 = A.

and if they did not have a starter, then the probability of not ordering dessert is 1 - 2/3 = 1/3 = B.