<PRE><B>Question 923544</B>
Let x=amount of time it takes 15 tractors to plow the field
If it takes 8 tractors 12 days to plow a field, then it will take 1 tractor 8*12 or 96 days to plow a field.  So the rate at which a tractor plows is 1/96 of a field/day and the rate at which 15 tractors plows is 15/96 of a field/day.
So our equation to solve is:
 
(15/96) of a field per day times x days =1 field plowed. or
(15/96)x=1 multiply each side by 96
15x=96
x=6.4 days

Another way:
It takes 8*12 =96 tractor-days to plow the field
1 tractor takes 96 days
2 tractors take 96/2=48 days
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8 tractors take 96/8=12 days
15 tractors take 96/15=6.4 days

Hope this helps---ptaylor

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