Question

A manufacturer knows that their items have a normally distributed lifespan, with a mean of 5.6 years, and standard deviation of 1.6 years.

If 25 items are picked at random, 1% of the time their mean life will be less than how many years?

Give your answer to one decimal place.

Answer 1

you can play around with Z-table stuff at

http://davidmlane.com/hyperstat/z_table.html

Answer 2

from a z-score table

1% of the population is approx. 2.33 s.d. below the mean

2.33 * 1.6 = ?