1. The cost per item at the supermarket follows an exponential distribution. There're many inexpensive items and few relatively expensive ones. The mean cost per item is $11.00. Determine the percentage of items that cost:
a. Less than $8.00?
b. Find out the 55th percentile. Forty five percent of supermarket items cost more than what amount?
2. A study of long-distance phone calls made from corporate offices of General Electric revealed length of the calls, in minutes, follows the normal probability distribution. The mean length of time per call was 3.7 minutes and standard deviation was 0.60 minutes.
(a) What fraction of calls last between 3.7 and 4.5 minutes?
(b) What fraction of calls last more than 4.5 minutes?
(c) What fraction of calls last between 4.5 and 5.5 minutes?
(d) What fraction of calls last between 3 and 5.5 minutes?
(e) As part of her report to the president, the director of communications would like to report length of longest (in duration) 5 percent of the calls. What is this time?
3. According to the government study among adults in 25- to 34-year age group, the mean amount spent per year on reading and entertainment is $1,999. Suppose that the distribution of amounts spent follows the normal distribution with the standard deviation of $574.
(a) What percent of adults spend more than $2,550 per year on reading as well as entertainment?
(b) What percent spend between $2,550 and $3,200 per year on reading as well as entertainment?
(c) What percent spend less than $1,100 per year on reading and entertainment?