Question

Life of Smoke Detectors The average lifetime of smoke detectors that a company manufactures is 5 years or months, and the standard deviation is 7 months. Find the probability that a random sample of 29 smoke detectors will have a mean lifetime between 56 and 63 months. Assume that the sample is taken from a large population and the correction factor can be ignored. Round the final answer to at least four decimal places and intermediate z-value calculations to two decimal places.

Answer 1

Ans:- M3 5 years = 12x5= 60 months X = mean liftime 6- 7 months. n=29 Standard error = z 12999 29 P(565*563) - P( 56-60 1'2999 l'2999 7 $112 Iz < 63-60 = P(-3.08 SZ< 2.31) = P(Z < 231) - P(Z3 -3:08) 0.9896 - 0.0010 0.9886