Assignment

The director of admissions at Kinzua University in Nova Scotia estimated the distribution of student admissions for the fall semester on the basis of past experience.

Admissions      Probability
1,030                   0.2
1,300                   0.2
1,660                   0.6

1. What is the expected number of admissions for the fall semester?

2. Compute the variance and the standard deviation of the number of admissions. (Round your standard deviation to 2 decimal places.)

The Internal Revenue Service is studying the category of charitable contributions. A sample of 34 returns is selected from young couples between the ages of 20 and 35 who had an adjusted gross income of more than $100,000. Of these 34 returns, 8 had charitable contributions of more than $1,000. Suppose 7 of these returns are selected for a comprehensive audit.

a. You should use the hypergeometric distribution is appropriate. Because

b. What is the probability exactly one of the seven audited had a charitable deduction of more than $1,000? (Round your answer to 4 decimal places.)
Probability

c. What is the probability at least one of the audited returns had a charitable contribution of more than $1,000? (Round your answer to 4 decimal places.)

Probability

According to the "January theory," if the stock market is up for the month of January, it will be up for the year. If it is down in January, it will be down for the year. According to an article in The Wall Street Journal, this theory held for 23 out of the last 34 years. Suppose there is no truth to this theory; that is, the probability it is either up or down is 0.5.

What is the probability this could occur by chance?

Customers experiencing technical difficulty with their internet cable hookup may call an 800 number for technical support. It takes the technician between 150 seconds and 13 minutes to resolve the problem. The distribution of this support time follows the uniform distribution.

a. What are the values for a and b in minutes?

b-1. What is the mean time to resolve the problem?

b-2. What is the standard deviation of the time?

c. What percent of the problems take more than 5 minutes to resolve?

d. Suppose we wish to find the middle 50% of the problem-solving times. What are the end points of these two times?

A normal population has a mean of 21 and a standard deviation of 6.

a. Compute the z value associated with 24.

b. What proportion of the population is between 21 and 24? (Round z-score computation to 2 decimal places and your final answer to 4 decimal places.)

c. What proportion of the population is less than 17?

Assume that the hourly cost to operate a commercial airplane follows the normal distribution with a mean of $5,870 per hour and a standard deviation of $417.

What is the operating cost for the lowest 5% of the airplanes?

The manufacturer of a laser printer reports the mean number of pages a cartridge will print before it needs replacing is 12,450. The distribution of pages printed per cartridge closely follows the normal probability distribution and the standard deviation is 570 pages. The manufacturer wants to provide guidelines to potential customers as to how long they can expect a cartridge to last.

How many pages should the manufacturer advertise for each cartridge if it wants to be correct 90 percent of the time? (Round z value to 2 decimal places. Round your answer to the nearest whole number.)

A study of long-distance phone calls made from General Electric Corporate Headquarters in Fairfield, Connecticut, revealed the length of the calls, in minutes, follows the normal probability distribution. The mean length of time per call was 3.80 minutes and the standard deviation was 0.70 minutes.

a. What fraction of the calls last between 3.80 and 4.50 minutes?

b. What fraction of the calls last more than 4.50 minutes?

c. What fraction of the calls last between 4.50 and 5.50 minutes?

d. What fraction of the calls last between 3.50 and 5.50 minutes?

e. As part of her report to the president, the director of communications would like to report the length of the longest (in duration) 6 percent of the calls. What is this time?

A student is taking two courses, history and math. The probability the student will pass the history course is .54, and the probability of passing the math course is .72. The probability of passing both is .40.

What is the probability of passing at least one?

All Seasons Plumbing has two service trucks that frequently need repair. If the probability the first truck is available is .80, the probability the second truck is available is .50, and the probability that both trucks are available is .40:

What is the probability neither truck is available?