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...

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=40.1σ=40.1 dollars. You would like to be 90% confident that your estimate is within 5 dollar(s) of average spending on the birthday parties. How many parents do you have to sample?