Statistics
posted by cain .
An article in a Health Magazine suggested getting a dog to encourage more regular walking. A researcher for the article found that the distribution of time spent walking dogs is approximately normally distributed with a mean of 38 minutes per day. However he also found that 13% of dog owners walk their dogs less than 20 minutes per day. What is the standard deviation of the time, in minutes, dog owners walk their dog per day?
I don't know how to find standard deviation. I tried to use the z score formula to solve for SD but there are too many unknown variables. There must be some calculator function (because doing it by hand is hard and takes forever) but I don't know it. Please help, thanks!

Statistics 
Scott
you have the mean
go to the zscore table and find 0.1300
... this will tell you the number of standard deviations
divide the number into 20 min to find the SD
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