In: Math
A restaurant wants to estimate the average bill paid by a party of two for dinner (service hours after 5 p.m.) They take a random sample of 100 bills and find that they average $80 with a standard deviation of $40. In making an 80% confidence interval for the parameter of interest, they should get a margin of error of about(Answer)?
Solution :
Given that,
Point estimate = sample mean = = 80
Population standard deviation = = 40
Sample size = n = 100
At 80% confidence level the z is ,
= 1 - 80% = 1 - 0.80 = 0.20
/ 2 = 0.20 / 2 = 0.10
Z/2 = Z0.10 = 1.28
Margin of error = E = Z/2* ( /n)
= 1.28 * (40 / 100)
= 5.12
Margin of error = E = 5.12
At 80% confidence interval estimate of the population mean is,
- E < < + E
80 - 5.12 < < 80 + 5.12
74.88 < < 85.12
(74.88, 85.12 )