Sample Size Determination

(Problems and Answers)

Minimum Life (alpha) = 0

Weibull slope (b) = 2.5?

2.  What sample size is needed for 100 Hrs. of running without any failures in order to have R = 0.999 with C = 0.90 to target 500 Hrs., if it is known that 

Minimum Life (alpha) = 0

Weibull slope (b) = 1.75?

3.  What sample size is needed in order that an estimated mean of 30 Hrs. be accurate within (+,- 10%) with one-sided confidence 90%, when the standard deviation is known to be 6 Hrs.?

4.  What sample size is needed in order that the standard deviation is accurate within (+,- 5%) with a one-sided confidence of 95%?

5.  What sample size is needed in order that an estimated skewness of 1 be accurate within (+,- 20%) with a one-sided confidence of 90%?

6.  What sample size is needed on materials A and B in order that a confidence of 99% (that A > B) be obtained from a mean life ratio of 1.75 when materials A and B both have Weibull slope 2.7?

6a. Answer question (6) at the B-10 level for a B-q life ratio of 1.75.

7.  What sample size is needed in order that the Weibull slope be accurate within (+,- 25%) with a one-sided confidence of 90%?

Answers to Practice Exercise Problems