A can do a certain work-in the same time in which B and C together can do it. If A and B together could do it in 10 days and C alone in 50 days, then B alone could do it in_________?

A. 15 days
B. 20 days
C. 25 days
D. 30 days

(A + B)’s 1 day’s work = 1/10; C’s 1 day’s work = 1/50 (A + B + C)’s 1 day’s work = 1/10 + 1/50 = 6/50 = 3/25 Also, A’s 1 day’s work = (B + C)’s 1 day’s work
From (i) and (ii), we get : 2 x (A’s 1 day’s work) = 3/25 As 1 day’s work = 3/50 B’s 1 day’s work = 1/10 – 3/50 = 2/50 = 1/25 So, B alone could do the work in 25 days.