At the USA open Tennis Championship a statistician keeps track of every serve that a player hits during the tournament.

At the USA 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 102 miles per hour (mph)and the standard deviation of the serve speeds was 13 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 89 mph and 128 mph?