Question 1033606: pizza king has found that the time it takes to deliver a pizza is normally distributed with mean of 22 minutes and standard deviation of 3 minutes. Pizza king wants to give away a free pizza to any customer who has to wait a long time to get its delivery. If pizza king only wants to give a free pizza to no more than 10% of its customers, how long should it set its delivery time for
Answer by wilft1(217)   (Show Source):
You can put this solution on YOUR website! shorter delivery time will be on the left of the z scale, whilst longer times will be on the right side. we are going to need to find out the numerical value for the last 10 percent on the right of the z scale, to do that, we will have to look up a z scale and find the number closest to 90 percent.
when we look on the z chart, the number closest to .9000 is .8997, with the z score of that being z = 1.28
using that number we will multiply the z score by S (standard deviation) then add the mean to get the number of minutes.
1.28 x 3 then + 22 = 25.84 minutes. assuming I understood the whole "10% of the customers" correctly
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