SOLUTION: person A takes 3 hours to work while person B takes 4 hours. how long does it take them when working together?

Question 550575: person A takes 3 hours to work while person B takes 4 hours. how long does it take them when working together?
Found 2 solutions by fcabanski, mathstutor494:
Answer by fcabanski(1391) (Show Source): You can put this solution on YOUR website!
Problems of this type come down to finding each person's work rate, adding the rates, then determining how long to complete the entire job.

A completes the whole job in 3 hours, and so completes 1/3 of the job per hour.
B completes the whole job in 4 hours, and so completes 1/4 of the job per hour.
Working together they complete 1/3 + 1/4 = 7/12 of the job per hour.

1 (the whole job) = rate * time. The rate is 7/12 job per hour, so:
1=7/12 + t

Divide both sides by 7/12:
1*12/7 = t (in hours)
12/7 = t (in hours) = approximately 1.7 hours = 1 hour 42 minutes.

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Answer by mathstutor494(120) (Show Source): You can put this solution on YOUR website!
Person A takes 3 hours to work, so he completes 1/3 work in 1 hr.
Similarly,Person B takes 4 hours to work, so he completes 1/4 work in 1 hr.

Working togther they complete 1/3+ 1/4 = 7/12 in 1 hr.
Hence total time taken to complete work = 12/7 hrs (Unitory Method)
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