SOLUTION: If 3 men dig ridges in 21 days. How many men will dig the same ridges in 7 days?

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Question 897729: If 3 men dig ridges in 21 days. How many men will dig the same ridges in 7 days?
Answer by josgarithmetic(39620) About Me  (Show Source):
You can put this solution on YOUR website!
1 job = "dig the ridges".
Let r = rate of doing the job for ONE man.
Let n = number of men asked in the problem.

RT=J for uniform rate of doing a job, rate time job.
3r%2A21=n%2Ar%2A7
Solve for n.