SOLUTION: A supermarket manager wishes to make an estimate of the average time in minutes a customer spends at the checkout counter. It is known from previous studies that the variance is 8.

Question 1193302: A supermarket manager wishes to make an estimate of the average time in minutes a customer spends at the checkout counter. It is known from previous studies that the variance is 8.1. How large a sample is required if she wants a 95% confidence interval for the population mean that extends no further than 1 minutes from the sample mean. Round up your answer to a whole number.
Answer by Boreal(15235) (Show Source): You can put this solution on YOUR website!
error=z(0.975)*change in mean/sigma/sqrt(n)
sigma=sqrt(V)=2.85
1=1.96*2.85/sqrt(n)
square both sides
1=3.8416*8.1/n
n=31.12=32, rounding up

RELATED QUESTIONS
A supermarket manager wishes to make an estimate of the average time in minutes a... (answered by jim_thompson5910)

The manager of a grocery store wishes to look at the efficiency of his staff. He takes a... (answered by ewatrrr)

1. A supermarket manager has determined that the amount of time customers spend in the... (answered by tommyt3rd)

A gym knows that each member, on average, spends 70 minutes at the gym per week, with a... (answered by VFBundy)

A gym knows that each member, on average, spends 50 minutes at the gym per week, with a... (answered by Boreal)

SafeRoad Stores is redesigning the checkout lanes in its stores throughout the country.... (answered by stanbon)

Checkout times in a Wal-Mart store follow a normal distribution with a mean time of 8... (answered by stanbon)

A statistical analysis of the wait time (in minutes) at the checkout line of a certain... (answered by robertb)

The shopping times were recorded for 64 randomly selected customers for a local... (answered by stanbon)