Question 412380
Karl can do 1/3 of job in 1 hour
brother can do 1/4 of the job in 1 hour
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Together they will do 1/3 + 1/4 of the job in 1 hour
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LCD = 12
they do 7/12 of the job in 1 hour
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they take 12/7 hours
=1.71 hours