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A and B can do a piece of work separately in 8 and 12 h. If they work alternate hours, A starting, when will the work be finished ?
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- 91/2 h
- 9 h
- 81/2 h
- 8 h
Correct Option: A
(A + B +)'s 2 h work = 1/8 + 1/12 = 5/24
(A + B)'s 8 h work = (5 x 8)/(24 x 2) = 5/6
Work done by A in 9th h = 1/8
Total work done upto 9th h = 5/6 + 1/8 = 23/24
Remaining wok = 1/24
B's 1 h work = 1/12
B can do 1/24 of the work = (1/24) x 12 = 1/2 h
So, both can finish the job in 91/2 h.
