SOLUTION: The length of time it takes to fill an order at a local sandwich shop is normally distributed with a mean of 4.1 minutes and a standard deviation of 1.3 minutes. The probability is

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Question 1187347: The length of time it takes to fill an order at a local sandwich shop is normally distributed with a mean of 4.1 minutes and a standard deviation of 1.3 minutes. The probability is 80% that the waiting time is greater than how long?

Answer by Boreal(15235) About Me  (Show Source):
You can put this solution on YOUR website!
you want the 20th percentile
invnorm function shows the z for that as -0.8416.
z=(x-mean)/sd
-0.84=(x-4.1)/1.3
-1.09=x-4.1
x=3 minutes.