SOLUTION: A farmer can plow a field in 24 hours. His son, with a larger plow, can plow it in 12 hours. The farmer asked that they work together so they could finish before the rain started.

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Question 1201657: A farmer can plow a field in 24 hours. His son, with a larger plow, can plow it in 12 hours. The farmer asked that they work together so they could finish before the rain started. It rained 7 hours later. Had they finished plowing before the rain?
Answer by ikleyn(52752) About Me  (Show Source):
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A farmer can plow a field in 24 hours. His son, with a larger plow,
can plow it in 12 hours. The farmer asked that they work together
so they could finish before the rain started. It rained 7 hours later.
Had they finished plowing before the rain?
~~~~~~~~~~~~~~~~~ 

The farmer's rate of work is  1%2F24  of the job per hour.

His son's rate of work is  1%2F12  of the job per hour.


Their combined rate of work is the sum

    1%2F24 + 1%2F12 = 1%2F24 + 2%2F24 = 3%2F24 = 1%2F8  of the job per hour.


In 7 hours, they will complete only  7%2F8  of the job - not the entire job.


ANSWER.  They will not complete the job in 7 hours - it requires 8 hours.

Solved.