Question

Suppose that the time required to complete a 1040R tax form is normally distributed with a mean of 90 minutes and a standard deviation of 10 minutes. What proportion of 1040R tax forms will be completed in less than 85 minutes? Round your answers to at least four decimal places.

Answer 1

Solution :

Given that ,

mean = = 90

standard deviation = = 10

P(X<85 ) = P[(X- ) / < (85-90) / 10]

= P(z <-0.5 )

Using z table

proportion = 0.3085