Probability (Intro, Mult/Add Rules, & Counting) Exercises

Question

Pollsters are concerned about declining levels of cooperation among persons contacted in surveys. A pollster contacts 102 people in the 18-21 age bracket and finds that 87 of them respond and 15 refuse to respond. When 252 people in the 22-29 age bracket are contacted, 236 respond and 16 refuse to respond. Assume that 1 of the 354 people is randomly selected. Find the probability of getting someone in the 22-29 age bracket OR someone who refused to respond.

Report the answer as a percent rounded to one decimal place accuracy. You need not enter the "%" symbol.

Answer 1

We want P(22-29 or ref) = P(22-29) + P(Ref) - P(22-29 and Ref) (The last term is that we don't want to count that group twice) Or you could add P(22-29) + P(18-21 and Ref) from the logic of the situation

We are talking about the probabilities based on the total number of people: 354

(1/354)(252 + 15)

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