The sampling distribution for a proportion has a formula for that ...

[ereecah]

The sampling distribution for a proportion has a formula for that standard error that involves using p. Yet when a confidence interval is calculated for a proportion, the standard error formula uses the sample proportion. Why do they differ?
 
  What will be an ideal response?

Question 2

Many Walmart stores have automotive departments where customers can buy tires, have their vehicles serviced, and obtain other automotive services.
 
  Recently, the manager at an Ohio Walmart collected data on the time customers had to wait to get the desired automotive service. Of the 500 cars in the sample, the shortest time any customer spent waiting was 3 minutes and the longest time was 183 minutes. Assuming that the manager wishes to develop a frequency distribution with 9 classes, which of the following would be an appropriate class width for each class?A) 10.50
  B) 19.99
  C) 20.00
  D) 3 to 23

[raili21]

Answer to Question 1

The correct way to calculate the standard error for a sampling distribution for a proportion is to use p in the formula. When calculating a confidence interval for a proportion, the problem is that we don't know what p is. The whole purpose of taking the sample and finding the confidence interval is to obtain an estimate of the value of p. The problem is that the standard error formula uses p, so that best that we can do is use the best estimate we have available in place of p. This best estimate is the sample proportion.

Answer to Question 2

C

[ereecah]

Excellent

[vickybb89]

Thanks for the timely response, appreciate it