The times to pop a regular bag of microwave popcorn without burning it are Normally distributed with a mean time of 140 seconds and a standard deviation of 20 seconds. The times to pop a mini bag of microwave popcorn
without burning it are Normally distributed with a mean time of 90 seconds and a standard deviation of 15
seconds. Suppose two independent random samples, 25 of each, are taken and the mean popping times are
calculated. Let R = the popping time of a randomly selected regular-sized bag and M = the popping time of a mini-
sized bag. Which of the following best describes the standard deviation of the sampling distribution of 5-7 ?
1 second
5 seconds
25 seconds
35 seconds