Calculating Wheat Field Yield Variance: A Quick Statistics Problem

[taffyleg]

For a sample of 100 wheat fields, the mean yield was 10 tons/acre and the standard deviation 2. Approximately how many fields out of the 100 should have yields in the 8 to 12 ton range? Show work.

 

[HallsofIvy]

But you haven't (shown your work, that is). What have you done on this? Do you know how to find the standard normal variable? Do you have a table of the normal probability distribution? If not, here's a good one on line:
http://people.hofstra.edu/Faculty/Stefan_Waner/RealWorld/normaltable.html