Q) To do a certain work, A and B work on alternate days with B beginning the work on the first day. A alone can complete the same work in 24 days. If the work gets completed in 11 1/3 days, then B alone can complete 7/9th part of the original work in:

a) 4 days              b) 6 days             c) 5 1/2 days                d) 4 1/2 days

Ans:

B starts the work and works on 1, 3, 5, 7, 9 and 11 days i.e. 6 days

Similarly, A works on 2, 4, 6, 8, 10, 1/3 of 12th day i.e. 5 1/3 days = 16/3 days

Work done by A in 1 day = 1/24

∴ Work done by A in 16/3 days = 16/3 x 1/24 = 2/9

∴ Balance work = 1 – 2/9 – 7/9 and we calculated above that B does it in 6 days

Hence, Answer is [B]

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