Question

The life of light bulbs is distributed normally. The variance of the lifetime is 400 and the mean lifetime of a bulb is 530 hours. Find the probability of a bulb lasting for at least 552 hours. Round your answer to four decimal places.

Answer 1

Solution :

Given that,

mean = =530

variance=400

standard deviation = = variance= 400=20

P(x >552 ) = 1 - P(x<552 )

= 1 - P[(x -) / < (552 -530) / 20]

= 1 - P(z <1.1 )

Using z table

= 1 -  0.8643

probability= 0.1357