Question

The life of light bulbs is distributed normally. The standard deviation of the lifetime is 20 hours and the mean lifetime of a bulb is 590 hours. Find the probability of a bulb lasting for at most 626 hours. Round your answer to four decimal places.

Answer 1

We have given the normal distribution

X : life time of the bulb

At most means less than equal to

we are asked to find

We find the z score for 626

So we are asked to find

We use z table because Z table always gives you the left side area

We look for row headed 1.8   and column headed .00

So we get the probability as 0.9641

Final answer

Probability of a bulb lasting for at most 626 hours = 0.9641

I hope this will help you :)