Question

The amount of time a certain brand of light bulb lasts is normally distribued with a mean of 1300 hours and a standard deviation of 60 hours. Out of 710 freshly installed light bulbs in a new large building, how many would be expected to last between 1240 hours and 1430 hours, to the nearest whole number?

Answer 1

You can play around with Z table stuff at
davidmlane.com/hyperstat/z_table.html