Question

Mean or Proportion?!

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

Here is the formula for confidence interval of a mean\[ \Large \overline x \pm z_{\alpha/2}\frac{\sigma}{\sqrt n}\]

Answer 2

Do you know what the symbols represent. Let me know, I will explain.

Answer 3

The quantity\[z _{\frac{ \alpha }{ 2 }} \] is called the "z-critical value." Know how to find this value for a 99% confidence interval?

Answer 4

If not, would you mind looking up "z critical value" on the Internet or in your textbook?

Answer 5

I am so lost, I still cannot understand. :(

Answer 6

Perl gave the formula. mathmale explained the z critical value.

\(\large \overline x \) is the mean.
\(\large \sigma\) is the standard deviation
\(\large n\) is the sample size.

Read the question, identify each value, then plug them into the formula.