Question

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.

Answer 1

The formula for the confidence interval is given by

Sample mean + z*[σ/√n], and
Sample mean - z*[σ/√n]

We have:
Sample mean = 23.95
n = 40 
σ = 2.55
z* for 99% confidence = 2.58

Substitute these values into the formula, we have

23.95 + (2.58)(2.55÷√40) = 24.99
23.95 - (2.58)(2.55÷√40) = 22.91

So the lower interval is 22.91 and the highest interval is 24.99