A & B can separately do a piece of work in 20 & 15 days. They worked together for 6 days, after which B was replaced by C. The work was finished in next 5 days. The no.of days in which C alone could do the work is
Choose the correct choice from the following
A) 10 days
B) 20 days
C) 30 days
D) 40 days
E) 50 days

Rationale: b worked for 6 days = > in 6 days b completed = 6 x 1 15 = 2 5 th work a worked for first 6 days and later 4 days = > in 10 days a completed = 10 x 1 20 = 1 2 of the work total work done by a and b = 2 5 + 1 2 = 4 + 5 10 = 9 10 balance work = 1 - 9 10 = 1 10 th of total work balance work was completed by c in 5 days c can do 1 / 10 of the work in 5 days . therefore c alone can do the work in 50 days . e
Answer: E