At the US Open Tennis Championship a Statistician Keeps Track of Every

Multiple Choice

At the U.S. Open Tennis Championship a statistician keeps track of every serve that a player hits during the tournament. The statistician reported that the mean serve speed was 100 miles per hour (mph) and the standard deviation of the serve speeds was 15 mph. If nothing is known about the shape of the distribution, what percentage of the player's serve speeds are less than 70 mph?

A) approximately 2.5%
B) at most 12.5%
C) at most 11%
D) at most 25%
E) approximately 5%