Suppose that the time required to complete a 1040R tax form

Suppose that the time required to complete a 1040R tax form is normally distributed with a mean of minutes and a standard deviation of minutes. What proportion of 1040R tax forms will be completed in at most minutes? Round your answer to at least four decimal places.

Solution

First find the z score using the formula:

Z=(x-mu)/sigma

Then find the required probability P(X<x)=P(Z<z) using z score table.