Question

You want to obtain a sample to estimate how much parents spend on their kids birthday parties. Based on previous study, you believe the population standard deviation is approximately σ=58.5σ=58.5 dollars. You would like to be 90% confident that your estimate is within 2.5 dollar(s) of average spending on the birthday parties. How many parents do you have to sample?

Answer 1

We are given the margin of error here as 2.5 dollars.

From standard normal tables, we have:
P(-1.645 < Z < 1.645) = 0.9

Therefore the margin of error here is computed as:

Putting all the above values, we get here:

Therefore 1482 is the required minimum sample size here.