A recent study showed that the length of time required for customers to resolve their computer issues with online support is normally distributed with a mean equal to 0.35 hours with a standard deviation of 0.2 hours. Given this information, what is the probability of resolution will take between 10 and 15 minutes?
A) About 0.13
B) Nearly 0.00
C) About 0.31
D) About 0.87

Question

Quizplus · Accepted Answer

To find the probability that resolution will take between 10 and 15 minutes, we first convert these times into hours (10 minutes = 1/6 hours, 15 minutes = 1/4 hours). Then, we calculate the Z-scores for these times using the formula Z = (X - mean) / standard deviation. For 10 minutes (0.1667 hours), Z = (0.1667 - 0.35) / 0.2 = -0.9165. For 15 minutes (0.25 hours), Z = (0.25 - 0.35) / 0.2 = -0.5. Looking these Z-scores up in a standard normal distribution table, we find the probabilities corresponding to these Z-scores and subtract the smaller from the larger to find the probability of a resolution time between 10 and 15 minutes, which is about 0.13.

A Recent Study Showed That the Length of Time Required