Question

A research marketer for an online retail store was interested in the number of times per month stay-at-home moms bought items from online retail stores. She found the mean is 15 items and the standard deviation is 3 items purchased from online retail stores each month.

Using the empirical rule, approximately what percent of stay-at-home moms bought more than 21 items from online retail stores each month?

2.50%
5.0%
10.0%
16.0%
95.0%

Answer 1

Mean = 15

SD = 3

P(X >21) = ?

21 is equal to the mean plus 2 x the SD ( 15 + 2x3 = 15 +6 = 21)

2 times the SD would be 95% ( Empirical rule)

For 95%, that means that 5% is above and below it.

5%/2 = 2.5% is below and 2.5% is above.

The answer is 2.5%