Question

2. In a destructive test of product quality, a briefcase manufacturer places each of a simple random sample of the day’s production in a viselike device and measures how many pounds it takes to crush the case. From past experience, the standard deviation has been found to be 21.5pounds. For 35 cases randomly selected from today’s production, the average breaking strength was 341.0 pounds. The upper confidence limit of 99% confidence interval for the mean breaking strength of the briefcases produced today would equal to;

Answer 1

2)

Solution :

Given that,

Point estimate = sample mean = = 341.0

Population standard deviation = = 21.5

Sample size = n = 35

At 99% confidence level the z is ,

= 1 - 99% = 1 - 0.99 = 0.01

Z = Z_0.01 = 2.326

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

= 2.326 * (21.5 / 35)

= 8.5

The upper confidence limit of 99% confidence interval of the population mean is,

+ E = 341 + 8.5 = 349.5

upper confidence limit = 349.5