Question

The average weight of a sample of 36 bags of oat cookies is 35 ounces. The population standard deviation is 4 ounces, a 95% confidence interval will be: Select one: a. 35 ± (1.33) b. 35 ± (1.31) c. 35 ± (1.35) d. 35 ± (1.32)

Answer 1

= Solution :

Given that,

Point estimate = sample mean = = 35

Population standard deviation =    = 4

Sample size n =36

At 95% confidence level the z is ,

= 1 - 95% = 1 - 0.95 = 0.05

/ 2 = 0.05 / 2 = 0.025

Z/2 = Z0.025 = 1.96   ( Using z table )

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

= 1.96 * ( 4/  36 )

= 1.31
At 95% confidence interval
is,

± E

35 ± (1.31)