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 of a particular player was 98 miles per hour (mph) and the standard deviation of the serve speeds was 9 mph. Assume that the statistician also gave us the information that the distribution of the serve speeds was mound-shaped and symmetric. What proportion of the player's serves was between 107 mph and 116 mph?
A) 0.1350
B) 0.270
C) 0.95
D) 116

Question

Quizplus · Accepted Answer

The serve speeds are normally distributed. The interval 107 mph to 116 mph is one standard deviation above the mean (98 + 9 = 107) to two standard deviations above the mean (98 + 2*9 = 116). Approximately 13.5% of data in a normal distribution lies between one and two standard deviations above the mean.

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