Question

A marketing firm wants to estimate how much root beer the average teenager drinks per year. A previous study found a standard deviation of 1.28 liters. How many teenagers must the firm interview in order to have a margin of error of at most 0.2 liter when constructing a 99% confidence interval?

Answer 1

Solution

standard deviation =   =1.28

Margin of error = E = 0.2

At 99% confidence level the z is,

= 1 - 99%

= 1 - 0.99 = 0.01

/2 = 0.005

Z/2 = 2.58

sample size = n = [Z/2* / E] 2

n = ( 2.58*1.28 /0.2 )2

n =272.64

Sample size = n =273