Correct Answer: Option C
(B + C)'s 1 day's work = {(1/9) +(1/12)} = 7/12.
Work done by B and C in 3 days ={(7/36) x 3} = 7/12.
Remaining work ={1 –(7/12)} = 5/12.
Now, 1/24 work is done by A in 1 day.
So, 5/12 work is done by A in {24 x (5/12)} = 10 days.
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