Question

You own a small storefront retail business and are interested in determining the average amount of money a typical customer spends per visit to your store. You take a random sample over the course of a month for 15 customers and find that the average dollar amount spent per transaction per customer is $86.485 with a standard deviation of $15.8647. Create a 99% confidence interval for the true average spent for all customers per transaction.

Question 2 options:

	1) ( 83.508 , 89.462 )
	2) ( 82.389 , 90.581 )
	3) ( -74.291 , 98.679 )
	4) ( 74.291 , 98.679 )
	5) ( 74.413 , 98.557 )

Question 3 (1 point)

You own a small storefront retail business and are interested in determining the average amount of money a typical customer spends per visit to your store. You take a random sample over the course of a month for 12 customers and find that the average dollar amount spent per transaction per customer is $116.194 with a standard deviation of $11.3781. Create a 90% confidence interval for the true average spent for all customers per transaction.

Question 3 options:

	1) ( 114.398 , 117.99 )
	2) ( 112.909 , 119.479 )
	3) ( -110.295 , 122.093 )
	4) ( 110.341 , 122.047 )
	5) ( 110.295 , 122.093 )

Question 4 (1 point)

You are tracking Chipotle Mexican Grill's stock price, attempting to figure out a good price point for entry into the market. You look at 49 random days over the course of a few months and see that the closing price has an average of $326.28 with a standard deviation of $16.167. You construct a 95% confidence interval for the average stock price to be (321.64, 330.92). Of the following choices, what is the appropriate interpretation of this interval?

Question 4 options:

	1) We are 95% confident the average daily closing price for any day is between $321.64 and $330.92
	2) We are certain that 95% of the daily closing prices will be between $321.64 and $330.92.
	3) We are 95% confident that the proportion of all days that have a closing price between $321.64 and $330.92 is 95%
	4) We cannot determine the proper interpretation of this interval.
	5) We are 95% confident the average daily closing price for the days monitored is between $321.64 and $330.92.

Question 5 (1 point)

A local pizza place claims that they average a delivery time of 7.13 minutes. To test this claim, you order 15 pizzas over the next month at random times on random days of the week. You calculate that the average delivery time is 8.52 minutes with a standard deviation of 1.801 minutes. You create a 95% confidence interval of (7.52, 9.52). Of those listed below, what is the best conclusion you can make?

Question 5 options:

	1) You are 95% confident that the average delivery time is less than 7.13 minutes.
	2) The percentage of pizzas that arrive around 7.13 minutes is 95%.
	3) We cannot determine the proper interpretation based on the information given.
	4) You are 95% confident that the average delivery time is greater than 7.13 minutes.
	5) The average delivery time does not significantly differ from 7.13 minutes.

Question 6 (1 point)

Researchers at a metals lab are testing a new alloy for use in high end electronics. The alloy is very expensive to make so their budget for testing is limited. The researchers need to estimate the average force required to bend a piece of the alloy to a 90 degree angle. From previous tests, the standard deviation is known to be 37.485 Newtons. In order to estimate the true mean within a margin of error of 10.125 Newtons with 90% confidence, how many samples would need to be tested?

Question 6 options:

	1) We do not have enough information to answer this question since we were not given the sample mean.
	2) 38
	3) 37
	4) 48
	5) 43

Question 7 (1 point)

The owner of a local supermarket wants to estimate the difference between the average number of gallons of milk sold per day on weekdays and weekends. The owner samples 20 weekdays and finds an average of 244.119 gallons of milk sold on those days with a standard deviation of 37.389. 23 Saturdays and Sundays are sampled and the average number of gallons sold is 303.89 with a standard deviation of 42.816. If a 99% confidence interval is calculated to estimate the difference between the average number of gallons sold on weekdays and weekends, what is the margin of error? Assume both population standard deviations are equal.

Question 7 options:

	1) 33.358
	2) 12.34947828
	3) 2.7011813
	4) 31.81
	5) 29.896

Answer 1

Question 2:

n = sample size = 15

Sample mean =

Sample standard deviation = s = 15.8647

Here population standard deviation is not known so we use t interval.

Confidence level = c = 0.99

99% confidence interval for the true average spent for all customers per transaction is

Where tc is t critical value for c = 0.99 and degrees of freedom = n - 1 = 15 - 1 = 14

tc = 2.977                   (from statistical table of t values)

           (Round to 3 decimal)

99% confidence interval for the true average spent for all customers per transaction is (74.290, 98.680)