Question

If A and B together can complete a work in 12 days, B and C together in 15 days and C and A together in 20 days, then in how many days can B alone complete the work :
A. 20 days
B. 24 days
C. 25 days
D. 30 days

Answer 1

Answer:

(A + B)’s 1 day’s work = \frac{1}{12}

(B + C)’s 1 day’s work = \frac{1}{15}

(C + A)’s 1 day’s work = \frac{1}{20}

On adding all above equations,

2(A + B + C)’s 1 day’s work = \frac{1}{12}+\frac{1}{15}+\frac{1}{20}

= \frac{5+4+3}{60} = \frac{1}{5}

∴ (A + B + C)’s 1 day’s work = \frac{1}{10}

∴ B’s 1 day’s work = \frac{1}{10}-\frac{1}{20} = \frac{2-1}{20} = \frac{1}{20}