Question

8. A, B and C can do a work in 12, 15 and 20 days respectively. They started working together but after 4 days A left.
In how many days will B and C complete the work?

Answer 1

Step-by-step explanation:

A does 1/12th of the work in a day.

B does 1/15th of the work in a day.

C does 1/20th of the work in a day.

So in two days that the three work together and they completed

(2/12) +(2/15) + (2/20) = (10/60) + (8/60) + (6/60) or (24/60) or 2/5th of the work. So what remains to be done is 3/5th of the work.

A and B together do (1/12) +(1/15) = (5/60) + (4/60) = 9/60 or 3/20th of the work in a day. So the two working together will take (3/5)/(3/20) = (3*20/(5*3) = 4 days.

C and B will complete the work in 4 days after A had left them.