Question

The life of light bulbs is distributed normally. The variance of the lifetime is 225 and the mean lifetime of a bulb is 520 hours. Find the probability of a bulb lasting for at most 533 hours. Round your answer to four decimal places.

Answer 1

Explanation:

= 520 , = 225,   = 15

a)

We want to find P(x 533 )

z = 0.8667

round to 2 decimals

z = 0.87

P(x 533 ) = P(z < 0.87 )

using z table we get

P(z < 0.87 ) = 0.8078

P(x 533 ) = P(z < 0.87 ) = 0.8078

Probability = 0.8078