Question

QUESTION 9 1 points Save Answer Past experience has indicated that the breaking strength of yarn used in manufacturing drapery material is normally distributed and that ơ-6.2 psi A randorm sample of nine specimens is tested, and the average breaking strength s found to be 7 psi The 95% confidence interval for the truc mean breaking strength is written as (A ; B). Find the value of A? round your answer to three digits. QUESTION 10 1 points Save Answer A normal population has a mean 100 and variance 25. How large must the sample size be if we want the standard deviation of the sample average to be at most 1.5? The sample size is an integer value.

Answer 1

9) Z for 95% confidence interval = Z_0.025 = 1.96

A

=X- ー20.025 *

  

6.2 = 19.7-1.96 *

   = 15.649 (ans)

10) sd = sqrt(25) = 5

Standard deviation of sampling distirbution= sd / sqrt(n)

or, 1.5 = 5 / sqrt(n)

or, n = 12 (ans)