Question

A can do a certain work in 15 days and B
can do same work in 18 days. They work together but A had left the work after some days and B finished the remaining work in 7 days . After how many days A had left the work ?

Answer 1

A can complete a work in 15 days
B can complete a same work in 18 days
Let the total work be 90 units
So A can do 6 units of work per day
Whereas B can do 5 units of work per day
Now
A and B worked together for some days with effeciency of 11 units per day (efficiency of both A and B)
Afterwards only B worked for 7 days (7×5=35units)
The remaining 90-35=55 units should have completed by both A and B with a one day efficiency of 11 units
That implies, 55/11=5 days
Therefore, A had left the work after 5 days.