Mean or Proportion?!

Question

1. Chips Ahoy wants to perform a study to determine the number of chocolate chips in their cookies. To that end, they collected a sample of 40 cookies. The mean of this sample is 23.95 chocolate chips. From past studies, we know that the standard deviation is 2.55 chocolate chips. Construct a 99% confidence interval of the mean of chocolate chips in all such cookies. The situation refers to a mean or proportion?

2. As a manager for an advertising company, you must plan a campaign designed to increase Twitter usage. A recent survey suggests that 85% of adults know what Twitter is. How many adults should you survey in order to be 90% confident that your estimate is within 5% of the true population proportion? The situation refers to a mean or proportion?

Answer 1

Both questions give context clues within the paragraph (stated immediately before the final sentences in each) to let you know whether or not the situation is referring to mean or proportion.

 

Question #1 refers to constructing a 99% confidence interval of the mean of chocolate chips in all such cookies, and you are given a sample number of cookies, the mean of the sample, and the standard deviation. 

 

Thus, this situation is referring to a mean.

 

Question #2 refers to finding the correct number of adults to survey to find the true population proportion, also stating that you should be 90% confident that your estimate is within 5% of said true population proportion.

 

Thus, this situation is referring to a proportion.