An oil change shop advertised to change oil within 15 minute

An oil change shop advertised to change oil within 15 minutes. Based on the data collected on a typical day, what is the probability that oil change will take 15 minutes or less time? Based on the data, do you think the business claim is valid? Explain why or why not. Class Interval Frequency 6 to 10 minutes 3 11 to 15 minutes 8 16 to 20 minutes 6 21 to 25 minutes 2 More than 25 Minutes 1

Solution

There are 3+8 = 11 change oils less than 15 minutes.

Thus,

P(less than 15 min) = 11/20 = 0.55 [ANSWER]

It seems that the business claim is not valid, because only about half of the services qualified for their claim.