5. The number of walnuts in a mass-produced bag is modeled by a normal distribution with a mean of 44
and a standard deviation of 5. Find the number of walnuts in a bag that has more walnuts than 80% of
the other bags.
Use Excel, and round your answer to the nearest integer. 48
Here, the mean, μ, is 44 and the standard deviation, σ, is 5. Let x be the number of walnuts in the bag.
The area to the left of x is 80%=0.80. Use Excel to find x.

6. A firm’s marketing manager believes that total sales for next year will follow the normal distribution,
with a mean of $3.2 million and a standard deviation of $250,000. Determine the sales level that has
only a 3% chance of being exceeded next year.

7. Suppose that the weight of navel oranges is normally distributed with a mean of μ=6 ounces and a
standard deviation of σ=0.8 ounces. Find the weight below that one can find the lightest 90% of all navel
oranges.
Use Excel, and round your answer to two decimal places. 7.03
Here, the mean, μ, is 6 and the standard deviation, σ, is 0.8. The area to the left of x is 90%=0.90. Use
Excel to find x.

8. A tire company finds the lifespan for one brand of its tires is normally distributed with a mean of
47,500 miles and a standard deviation of 3,000 miles. What mileage would correspond to the the highest
3% of the tires?

Use Excel, and round your answer to the nearest integer. 53,142
Here, the mean, μ, is 47,500 and the standard deviation, σ, is 3,000. Let x be the minimum number of
miles for a tire to be in the top 3%. The area to the right of x is 3%=0.03. So, the area to the left of x is
1−0.03=0.97. Use Excel to find x.
1. Open Excel. Click on an empty cell. Type =NORM.INV(0.97,47500,3000) and press ENTER.
The answer, rounded to the nearest integer, is x≈53,142. Thus, the approximate number of miles for the
highest 3% of the tires is 53,142 miles.
1.
The average credit card debt owed by Americans is $6375, with a standard deviation of $1200.
Suppose a random sample of 36 Americans is selected. Identify each of the following:
1.
6375