Question

two men can do a piece of work in 6 hours and 4 hours respectively.After the first has worked for 2 hours,he is joined by the other.By when should the work be completed.
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Answer 1

Let the man A say works for 6hrs. Then in 1 hr the man A can do 1/6 th part of work. Similarly the other man B say works for 4 hrs. Then the man B can do 1/4 th part of work in 1 hr. So together A & B can do(1/6+1/4=5/12th part of work in 1 hr.

Now A starts the work and in 2 hrs completes 2×1/6=1/3rd part of work . The remaining work left is (1-1/3=2/3rd part). Now B joins, So both A & B complete 5/12 th part of work in 1 hr, total work complete in 1÷5/12=12/5 hrs , the remaining 2/3rd part complete in 12/5×2/3=24/15=1hr & 9×60/15=1hr36 mins.

Answer 2

The work would completed by 6 hours because one had joined other