10. The time required for an automotive center to complete an oil change service on an automobile approximately follows a normal distribution, with a mean of 19 minutes and a standard deviation of 3.5 minutes. (a) The automotive center guarantees customers that the service will take no longer than 20 minutes. If it does take longer, the customer will receive the service for half-price. What percent of customers receive the service for half-price? (b) If the automotive center does not want to give the discount to more than 3% of its customers, how long should it make the guaranteed time limit? Click the icon to view a table of areas under the normal curve. (a) The percent of customers that receive the service for half-price is (Round to two decimal places as needed.) %. (b) The guaranteed time limit is minutes. (Round up to the nearest minute.)

3. At a land farm, a farmer desired to test the effect of a given fertilizer on soybean production. He chose 24 plots of land of which are equal surface area. He treated 12 plots with the fertilizer and the others were untreated. Otherwise the conditions were the same. The treated plots produced soybean with mean yield 5.1 bushels and a standard deviation of 0.36 bushels, while the untreated plots had mean yield 4.8 bushels and a standard deviation of 0.40 bushels. (a) Can we conclude that there is a significant improvement in soybean production because of the fertilizer if a significance level of 1% is used? (b) What is the P-value of the test?

Suppose that water usages in American showers are normally distributed, with an average shower using 20 gallons, and a standard deviation of 3.2 gallons. Estimate the percentage of showers that used (a) between 13.6 and 26.4 gallons. % (b) more than 26.4 gallons. % (c) less than 10.4 gallons. % (d) between 16.8 and 29.6 gallons. %

12. (Two Samples) According to a survey, the mean price of gasoline in the United States was $1.20 per gallon in 1995 and $1.10 per gallon in 1994. (U.S. News & World Report, June 12, 1995). Suppose these means were based on random samples of 100 gasoline stations for 1995 and 120 gasoline stations for 1994. Also, assume that the sample standard deviations were $0.11 for 1995 and $0.10 for 1994. a. Construct a 98% confidence interval for the difference between the mean gasoline prices for 1995 & 1994. b. Test at the 1% significance level if the mean gasoline price was higher in 1995 than in 1994.

15. The Exotic Fruit Juice Co. sell cartons of Passion Fruit and Orange fruit juice. The amount of liquid in each carton is normally distributed with a mean of 266ml and a standard deviation of 20ml. Cartons containing more than 300ml produce no profit. What percentage of cartons will this be?

According to the Empirical Rule, in a Normal Distribution of data you will have percent of the data within 1 standard deviation of the mean, percent of the data within 2 standard deviation of the mean, and percent of the data within 3 standard deviation of the mean.

1- Assume that the mean hourly cost to operate a commercial airplane follows a normal distribution with a mean of $2100 per hour and a standard deviation of $250. Determine the lowest 6% of the operating cost.