The speed of college tennis player Jaron Jackson's first serve averages 125 mph, with a standard deviation of 4 mph.If the distribution of service speeds is normal, what proportion of Jaron's serves will be between 120 and 130 mph?
A).6232
B).8421
C).9736
D).7888
E).7226

Question

Quizplus · Accepted Answer

To find the proportion of serves between 120 and 130 mph, we calculate the z-scores for 120 and 130 mph. The z-score for 120 mph is (120-125)/4 = -1.25, and for 130 mph is (130-125)/4 = 1.25. Using the standard normal distribution table, the proportion between these z-scores is approximately 0.7888.

The Speed of College Tennis Player Jaron Jackson's First Serve