( Solved) A and B working alone can do a work in 20 days and 15 days respectively. They started the work together but B left after sometime and A finished remaining work in 6 days. Find after how many days from start B left the work ?

 Question:

A and B working alone can do a work in 20 days and 15 days respectively. They started the work together but B left after sometime and A finished remaining work in 6 days. Find after how many days from start B left the work ?

Solution:

Efficiency Total work 

3 - A - 20

                         =     60

4 - B - 15

Here,

3+4=7 and A+B=60

Working done by A in last 6 days =6×3=18

Remaining done by A+B=60

Here, A=18 days

A+B=60

18+B=60

B=60-18

B=42 days

B left the work after = 42/7 = 6 days