let m be the mean, and
let s be the standard deviation
(11 - m)/s = -3
11-m = -3s
(16-m)/s = 3
16-m = 3s
add them : 27 - 2m=0
m = 13.5
3s = 16-13.5 = 2.5
Using my favourite normal distribution calculator:
http://davidmlane.com/hyperstat/z_table.html
I get .305
The time it takes me to wash the dishes is uniformly distributed between 11 minutes and 16 minutes.
What is the probability that washing dishes tonight will take me between 13 and 15 minutes?
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