(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 ….. (i)
A’s 1 day’s work = (B + C)’s 1 day’s work …. (ii)
From (i) and (ii), we get: 2 x (A’s 1 day’s work) = 3/25
=> A’s 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.