Question

You measure 43 textbooks' weights, and find they have a mean weight of 72 ounces. Assume the population standard deviation is 2.7 ounces. Based on this, construct a 90% confidence interval for the true population mean textbook weight.

Give your answers as decimals, to two places

___________ < ? < _______

Answer 1

Solution :

Given that,

= 72

= 2.7

n = 43

At 90% confidence level the z is ,

  = 1 - 90% = 1 - 0.90 = 0.10

/ 2 = 0.10 / 2 = 0.05

Z_/2 = Z_0.05 = 1.645

Margin of error = E = Z_/2* (/n)

= 1.645 * (2.7 / 43)

= 0.68

At 90% confidence interval estimate of the population mean is,

- E < < + E

72 - 0.68 < < 72 + 0.68

71.32 < < 72.68

(71.32 , 72.68)