Question

A can complete a project in 20 days and b can complete the same project in 30 days. if a and b start working on the project together and a quits 10 days before the project is completed, in how many days will the project be completed?

Answer 1

Let's see the answer

If a completes a project in 20 days , Hence the work done by a in each day will be 1/20

If b completes a project in 30 days , Hence the work done by b in each day will be 1/30

Now let's take the days required to complete the project if they work together as x
So the days required to complete the project
in one day will be 1/x

So according to the given conditions

1/20 + 1/30 = 1/x
30 + 20/600 = 1/x
50/600 = 1/x
50x = 600
x = 600/50
x = 12

Hence the days required or the project will be completed in 12 days

Hope it helps

Answer 2

Great explanation Casper!! Kudos!!

There is a trick here. Its metioned that 10 days before the project is completed A quits. I thought we can easily find when A quits. If A & B work together, they will complete the work in 12 days. So after 2 days A quits & B has to work for 25 more days to complete the work & hence my answer was 27.

Any how good question.