posted by HELPME .
the life of electric bulbs has a normal distribution with a mean of 35 months and a standard deviation of 4 months. What should the warranty period be if the company that manufactures these bulbs does not want to replace more than 2% of the bulbs?
Z = (score-mean)/SD
Find table in the back of your statistics text labeled something like "areas under normal distribution" to find the proportion (.02) and its Z score. Insert the value in the above equation and solve for the score. Remember that the Z score will be negative.
Here mean = 35
we have asked that
see normal table
It is z=2.05
remember it is standard normal table value but we have to convert it for x variable for which mean is 35 and s.d. is 4.
do the inverse operation for which we convert x into z.
rounding off it will be 48.
That is answer is 48.