Question

You own a small storefront retail business and are interested in determining the average amount of...

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 $119.375 with a standard deviation of $12.1991. Create a 95% confidence interval for the true average spent for all customers per transaction.

Question 1 options:

1)

( 116.225 , 122.525 )

2)

( 112.663 , 126.087 )

3)

( 112.619 , 126.131 )

4)

( -112.619 , 126.131 )

5)

( 117.23 , 121.52 )

Question 2 (1 point)

Suppose you want to determine the average height of basketball players in the NCAA Division I. In a random sample of 26 players, the sample average is 70.71 inches with a standard deviation of 6.669 inches. A 99% confidence interval for the average height is (67.06, 74.36). Which of the following is an appropriate interpretation of this interval?

Question 2 options:

1)

We are certain that 99% of the average heights of all basketball players will be between 67.06 and 74.36 inches.

2)

We are 99% confident that the average height of all NCAA D-I basketball players is between 67.06 and 74.36 inches.

3)

We are 99% confident that the proportion of all NCAA D-I basketball players heights is between 67.06 and 74.36 inches.

4)

We cannot determine the proper interpretation of this interval.

5)

We are 99% confident that the average height of all NCAA D-I basketball players surveyed is between 67.06 and 74.36 inches.

Question 3 (1 point)

Independent random samples are taken at a university to compare the average GPA of seniors to the average GPA of sophomores. Given a 99% confidence interval for the difference between the true average GPAs (seniors - sophomores) of (-0.58, 0.6), what can you conclude?

Question 3 options:

1)

We do not have enough information to make a conclusion.

2)

We are 99% confident that the average GPA of seniors is less than the average GPA of sophomores.

3)

We are 99% confident that the average GPA of seniors is greater than the average GPA of sophomores.

4)

We are 99% confident that the difference between the two sample GPAs falls within the interval.

5)

There is no significant difference between the true average GPA for seniors and sophomores.

Homework Answers

Answer #1

1)

sample mean 'x̄= 119.375
sample size   n= 15.00
sample std deviation s= 12.20
std error 'sx=s/√n= 3.1498
for 95% CI; and 14 df, value of t= 2.145
margin of error E=t*std error    = 6.756
lower bound=sample mean-E = 112.619
Upper bound=sample mean+E = 126.131
from above 95% confidence interval for population mean =(112.62,126.13)

correct option is": ( 112.619 , 126.131 )

2)

We are 99% confident that the average height of all NCAA D-I basketball players is between 67.06 and 74.36 inches.

3)since 0 is in the interval:

There is no significant difference between the true average GPA for seniors and sophomores

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