Question

A market research company employs a large number of typists to enter data into a computer. The time it takes for new typists to learn the computer system is known to have a normal distribution with a mean of 90 minutes and a standard deviation of 18 minutes. What is the proportion of new typists who take more than two hours to learn the computer system?

Answer 1

Below is the way you do this on a TI-83 plus or similar

Go to the `Distr` menu (second-VARS) and choose NormalCdf

NormalCdf works with the following parameters:
`low` =lower boundary
`high` =upper boundary (or choose a very large number)
`mean` or average
`STD` standard deviation

So you fill in:

`"NormalCdf" (120,10^99,90,18)` and you get `~~0.0478`