Question

You measure 43 textbooks' weights, and find they have a mean weight of 32 ounces. Assume the population standard deviation is 2.2 ounces. Based on this, construct a 90% confidence interval for the true population mean textbook weight.

Give your answers as decimals, to two places

? < μμ < ?

Answer 1

Solution :

Given that,

Point estimate = sample mean = = 32

Population standard deviation =    = 2.2
Sample size = n =43

At 90% confidence level

= 1 - 90%  

= 1 - 0.90 =0.10

/2 = 0.05

Z/2 = Z0.05 = 1.645

Margin of error = E = Z/2    * ( /n)

= 1.645 * ( 2.2/  43 )

= 0.55
At 90% confidence interval estimate of the population mean
is,

- E < < + E

32 -0.55 <   < 32 + 0.55

31.45 <   < 32.55