Question

A certain brand of flood lamp has a lifetime that is normally distributed with a mean of 3750 hours and a standard deviation of 300 hours. What lifetime should the manufacturer advertise for these lamps so that only 2% of the lamps will burn out before the advertised lifetime?

Answer 1

look in z-table to find the z-score for .02 --> P(x<.02)

Let L be lifetime:
z = (L-3750)/300

solve for L