Question

The mean lifetime of a tire is 42 months with a variance of 49.

If 145 tires are sampled, what is the probability that the mean of the sample would be greater than 42.8 months? Round your answer to four decimal places.

Answer 1

Solution :

Given that ,

mean = = 42

standard deviation = = 7

= / n = 7 / 145 = 0.5813

P( > 42.8) = 1 - P( < 42.8)

= 1 - P[( - ) / < (42.8 - 42) / 0.5813]

= 1 - P(z < 1.38)

= 1 - 0.9162

= 0.0838

Probability = 0.08