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Homework answers / question archive / Question1)What is the variance of the distribution? Question 2 Which shape describes a Poisson distribution? Question 3 A statistics professor receives an average of five e-mail messages per day from students

**Question1)**What is the variance of the distribution?

**Question 2**

Which shape describes a Poisson distribution?

**Question 3**

A statistics professor receives an average of five e-mail messages per day from students. Assume the number of messages approximates a Poisson distribution. What is the probability that on a randomly selected day she will have no messages?

**Question 4**

A true/false test consists of six questions. If you guess the answer to each question, what is the probability of getting all six questions correct?

**Question 5**

What is the variance of the distribution?

**Question 6**

A company is studying the number of monthly absences among its 125 employees. The following probability distribution shows the likelihood that people were absent 0, 1, 2, 3, 4, or 5 days last month.

What is the standard deviation of the number of days absent?

**Question 7**

A machine shop has 100 drill presses and other machines in constant use. The probability that a machine will become inoperative during a given day is 0.002. During some days, no machines are inoperative, but during some days, one, two, three, or more are broken down. What is the probability that fewer than two machines will be inoperative during a particular day?

**CorrectQuestion 8**

David's gasoline station offers 4 cents off per gallon if the customer pays in cash and does not use a credit card. Past evidence indicates that 40% of all customers pay in cash. During a one-hour period, 15 customers buy gasoline at this station. This situation is an example of what type of discrete probability distribution?

**Question 9**

The following is a Poisson probability distribution with µ = 0.1.

The variance of the distribution is ______.

**Question 10**

What is the mean of the distribution?

**Question 11**

The employees of Cartwright Manufacturing are awarded efficiency ratings. The distribution of the ratings approximates a normal distribution. The mean is 400, the standard deviation 50. What is the area under the normal curve between 400 and 482?

**Question 12**

The annual commissions per salesperson employed by a retailer of mobile communication devices averaged $40,000, with a standard deviation of $5,000. What percent of the salespersons earn between $32,000 and $42,000?

**Question 13**

An accelerated life test on a large number of type-D alkaline batteries revealed that the mean life for a particular use before they failed is 19.0 hours. The distribution of the lives approximated a normal distribution. The standard deviation of the distribution was 1.2 hours. About 95.44% of the batteries failed between what two values?

**Question 14**

What is the area under the normal curve between *z* = 0.0 and *z* = 1.79?

**Question 15**

Ball-Bearings, Inc. produces ball bearings automatically on a Kronar BBX machine. For one of the ball bearings, the mean diameter is set at 20.00 mm (millimeters). The standard deviation of the production over a long period of time was computed to be 0.150 mm. What percent of the ball bearings will have diameters of 20.27 mm or more?

**Question 16**

The mean of a normal distribution is 400 pounds. The standard deviation is 10 pounds. What is the probability of a weight between 415 pounds and the mean of 400 pounds?

**Question 17**

The shape of any uniform probability distribution is ____________.

**Question 18**

Two normal distributions are compared. One has a mean of 10 and a standard deviation of 10. The second normal distribution has a mean of 10 and a standard deviation of 2. Which of the following is true?

**Question 19**

The average score of 100 students taking a statistics final was 70, with a standard deviation of 7. Assuming a normal distribution, what is the probability that a student scored 90 or higher?

**Question 20**

The mean score of a college entrance test is 500; the standard deviation is 75. The scores are normally distributed. What percent of the students scored below 320?

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