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!
you have the mean
go to the z-score table and find 0.1300
... this will tell you the number of standard deviations
divide the number into 20 min to find the SD