Question

A random sample of 30 lunch orders at noodles and company showed a mean bill of $10.36 with a standard deviation of $5.31. find the 95 percent confidence interval for the mean bill of all lunch orders.

Answer 1

The formula for calculating the Confidence Interval is as follows:

Confidence Interval = x +- (z*s)/√N

Where:

x = mean = 10.36

z = taken from standard normal distribution table based on 95% confidence level = 1.96

s = standard deviation = 5.31

N = sample size = 30

Substituting know values on the equation:

Confidence Interval = 10.36 +- ( 1.96 * 5.31) / √30

Confidence Interval = 8.46 and 12.26

Hence the bill of lunch orders ranges from 8.46 to 12.26.