Question

Papa Fred's Pizza has found that the menu time to deliver a pizza is 21.2 minutes with a

standard deviation of 6.1 minutes. They want to have a guaranteed delivery time. In order to
deliver 99% within the guaranteed time you need to find the time represented by the 99
percentile. What is this value?

Answer 1

That time is 35.4 minutes.

Explanation:

The mean time of delivery follows a Normal Distribution pattern.

So we need to apply Z-scores to find out.

99% confidence in delivery time means P(z > value) = 0.01 = 1%

So z > 2.325

so. Pr [ (x - 21.2) / 6.1 > 2.325 ] = 1%

so x > 2.325*6.1 + 21.2

x > 35.3825 minutes would be out of the 99th percentile