Hi
I'll make two assumptions;
1. By 2 "spreadsheets" you mean 2 worksheets within the same workbook,
one called Mileage and one called Accidents
2. Every mileage entry has a corresponding Accident entry, so your two
worksheets have a range of data with the same number of rows and
columns.

Create a third sheet called "Accidents Per Million Miles"
In Cell A2 of this sheet:
1. Type =
2. Go to the "Accidents" sheet and click on cell C9 (which is where you
say the Accidents data starts)
3. type *1,000,000/
4. Go to the "mileage" sheet and click on cell C8 (which is where you
say the Mileage data starts)
5. Press return
This will give you your accidents per million miles for the first
mileage/accident numbers.

To get all the other accidents per million miles numbers drag the
formula you just created across the required number of columns (click
on the little square at the bottom right of the cell with your mouse
and drag) then, without letting go of the mouseclick, drag down the
formula the number of rows you need.

regards
Paul