Business Statistics
Assignment 3
1. 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?: About 0.82%
2. The weekly incomes of a large group of executives are normally
distributed with a mean of $2,000 and a standard deviation of
$100. What is the z-score for an income of $2,100: 1.00
3. The mean amount spent by a family of four on food is $500 per
month with a standard deviation of $75. Assuming that the food
costs are normally distributed , what is the probability that a
family spends less than $410 per month?: 0.1151
4. A new extended-life light bulb has an average life of 750
hours, with a standard deviation of 50 hours. If the life of these
light bulbs approximates a normal distribution, about what
percent of the distribution will be between 600 hours and 900
hours?: 99.47%
5. A study of a company's practice regarding the payment of
invoices revealed that an invoice was paid an average of 20 days
after it was received. The stan-dard deviation equaled five days.
Assuming that the distribution is normal, what percent of the
invoices were paid within 15 days?: 15.87%
6. An accelerated life test on a large number of type-D alkaline
batteries re-vealed 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 1.2
hours. About 95.44% of the batteries failed between what two
values?: 16.6 and 21.4
7. 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?: 0.4332
8. Which of following is true in a normal distribution?: The mean divides the
distribution into two equal areas
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Assignment 3
1. 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?: About 0.82%
2. The weekly incomes of a large group of executives are normally
distributed with a mean of $2,000 and a standard deviation of
$100. What is the z-score for an income of $2,100: 1.00
3. The mean amount spent by a family of four on food is $500 per
month with a standard deviation of $75. Assuming that the food
costs are normally distributed , what is the probability that a
family spends less than $410 per month?: 0.1151
4. A new extended-life light bulb has an average life of 750
hours, with a standard deviation of 50 hours. If the life of these
light bulbs approximates a normal distribution, about what
percent of the distribution will be between 600 hours and 900
hours?: 99.47%
5. A study of a company's practice regarding the payment of
invoices revealed that an invoice was paid an average of 20 days
after it was received. The stan-dard deviation equaled five days.
Assuming that the distribution is normal, what percent of the
invoices were paid within 15 days?: 15.87%
6. An accelerated life test on a large number of type-D alkaline
batteries re-vealed 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 1.2
hours. About 95.44% of the batteries failed between what two
values?: 16.6 and 21.4
7. 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?: 0.4332
8. Which of following is true in a normal distribution?: The mean divides the
distribution into two equal areas
1/
4
