A and B can do a work in 8 days, B and C can do the same work in 12 days. A, B and C together can finish it in 6 days. A and C together will do it in

A 18 days

B 8 days

C 3 days

D 4 days

E 5 days

Solution

Correct Answer: Option B

Let work done by (A + C) in 1 day be x

∵ A, B and C together can finish a work in 6 days

∴(A + B + C)'s 1 day's work = 1/6

Similarly, (A + B)'s 1 day's work = 1/8

(B + C)'s 1 day's work = 1/12

Work done by [(A + B) + (B + C) + (A + C)] in 1 day = 2 × work done by (A + B + C) in 1 day

∴(A + C)'s 1 day's work = 2 × work done by (A + B + C) in 1 day - Work done by [(A + B) + (B + C)]in 1 day

∴(A + C)'s 1 day's work = \(2 \times \frac{1}{6} - \left( {\frac{1}{8} + \frac{1}{{12}}} \right)\)

= 3/24

= 1/8

So, A and C together will do the work in 8 days.

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