A and B can do a work in 12 days, B and C in 15 days and A, B and C together take 10 days. Find the number of days taken by B alone.

20 24 60 90

20

Adding the efficiencies, (A + B) + (B + C) = 9 (A + B + C)  +   B = 9              6     +   B = 9                         B = 3 Time taken by B alone = \(\frac{Total \; Work}{Efficiency}\)                                  = \(\frac{60}{3}\) = 20 days