Question

Let X denote the lifetime of a machine component with an exponential distribution. The mean time for the component failure is 2500 hours.

Required:
What is the probability that the lifetime exceeds the mean time by more than 1 standard deviations?

Answer 1

15.8 % ???

at z = 1 p=.8413

I guess the question is asking 1-.8413 = 15.8 %

Explanation: