Question

You measure 42 textbooks' weights, and find they have a mean weight of 74 ounces. Assume the population standard deviation is 11.4 ounces. Based on this, construct a 90% confidence interval for the true population mean textbook weight. Give your answers as decimals, to two places

_____< μ<______

Answer 1

Solution

Given that,

= 74

= 11.4

n = 42

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 * ( 11.4 / 42 )

= 2.89

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

- E < < + E

74 - 2.89 < < 74 + 2.89

71.11 < < 76.89

(71.11 ,76.89)