Finite: Probability

Question

A hat has 5 slips of paper numbered 1, 2, 3, 4, 5. A slip of paper is selected at random and its number noted and the slip is not replaced. A second slip of paper is selected at random.

(a) What is the probability that an odd number was selected both times?

(b) What is the probability that the numbers selected sum to 6?

Answer 1

Hello Nathan,

If you pick two numbers, you want to multiply the probability for each step together.

a) Find the probability of picking an odd number for the first number. Then take out one odd number and find the probability of picking another odd number. Multiply your 2 probabilities together to get the answer.

b) Sum means add so you want two numbers that add to 6. You could pick a 1 and then a 5, a 2 and then a 4, a 4 and then a 2, or a 5 and then a 1.

Find the probability of picking each of those 4 combinations. (They will all have the same probability.) For example, what is the probability of picking a 1 and then a 5? Find the probability of picking a 1. Then remove the 1 and find the probability of picking a 5 as the second number. Multiply the probabilities together to get the probability of picking a 1 and then a 5. It is the same rule used in part a.

Do this for the other 3 combinations. Then add your 4 probabilities together (or multiply one probability by 4) to get the answer.