Question

The print on the package of -watt General Electric soft-white light-bulbs says that these bulbs have an average life of hours. Assume that the lives of all such bulbs have a normal distribution with a mean of hours and a standard deviation of hours. Find the probability that the mean life of a random sample of such bulbs will be

Answer 1

Hi your question is incomplete attached below is the complete question

answer : p ( X < 725 ) = 0.0116

Explanation:

Given data:

Average life of bulbs (μ ) = 750 hours

standard deviation (б ) = 55 hours

n ( sample size ) = 25

X = 725

Probability that the mean life of a random sample of 25 bulbs will be less than725 hours

p ( X < 725 ) = p (( X - μ )/ б √n < 725 - 750 / 55√25 )

= P ( Z > - 2.27 )

Hence P ( X < 725 ) = 0.0116 ( using Z-table )