Question

27) A fast food restaurant wants to know about how long, on average, a customer spends waiting in a drive-thru from the time their order ends to the time that they get their food. To investigate this, the restaurant takes a random sample of 36 cars and finds that it takes an average of 2.4 minutes. Suppose the restaurant knows that drive-thru times have a population standard deviation of 7 minutes. Calculate a 95% Confidence Interval for drive-thru times: (5 points)

Answer 1

Solution :

Given that,

Z$\alpha$/2 = Z_0.025 = 1.96

Margin of error = E = Z$\alpha$/2 * ( $\sigma$ /$\sqrt$n)

= 1.96 * ( 0.7 /  $\sqrt$36 )

= 0.23

At 95% confidence interval estimate of the population mean is,

  ± E

T

= 2.4  ± 0.23

= ( 2.17, 2.63 )