statistics
posted by Anonymous .
The number of hours that college students sleep on a week night is approximated by a normal curve with a mean of 7 hours and a standard deviation of 1.7 hours. Answer the question below using a z table:
On a week night, what percentage of students sleep between 5 and 10 hours

Perfectly suited for David Lane's great stats calculator
Just enter the values from your problem
http://davidmlane.com/hyperstat/z_table.html
I get 84.15%
If you must use your tables,
zscore for 10 = (107)/1.7 = 1.7647
zscore for 5 = (57)/1.7 = 1.17647
look up probability for 1.7647 in your tables
look up probability ofr 1.17647
subtract the two values to get .8415
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