You are interested in finding how many hours a person is willing to wait for a plane. It is found that the time people are willing to wait has a μ = 5.2 and a σ = 1.1. What is the probability a person is willing to wait more than seven hours?Using the standard score formula, z = ( x − μ ) / σ , the z-score equals to two decimal places 1.64, which corresponds to a probability of 0.9495 on my z-score tables. However, on the answer key provided, it states the probability is 0.0505 or what would correspond to a z-score of −1.64.Is this a trick of the wording involved in the question or are my z-tables (or standard score formula) wrong?

Question

You are interested in finding how many hours a person is willing to wait for a plane. It is found that the time people are willing to wait has a       μ    =  5.2 and a       σ    =  1.1. What is the probability a person is willing to wait more than seven hours?Using the standard score formula,   z  =  (  x  −      μ    )      /        σ  , the z-score equals to two decimal places 1.64, which corresponds to a probability of 0.9495 on my z-score tables. However, on the answer key provided, it states the probability is 0.0505 or what would correspond to a z-score of −1.64.Is this a trick of the wording involved in the question or are my z-tables (or standard score formula) wrong?

tykoyz · Accepted Answer

You&#039;ve computed correctly, but interpreted the number incorrectly. What you&#039;ve found is the probability that someone is willing to wait at most 7 hours; the probability you want is  1  −  0.9495  =  0.0505as the answer key states.