Question

X and Y can do a piece of work in 20 days and 12 days respectively. X started the work alone and then after 4 days Y joined him till the completion of the work. How long did the work last?

Options

• 6 days

• 10 days

• 15 days

• 20 days

Answer 1

10 days

Explanation:

Work done by X in 4 days = `(1/20 xx 4) = 1/5`

Remaming work = `(1 - 1/5) = 4/5`

(X + Y)’s 1 day’s work = `(1/20 + 1/12) = 8/60 = 2/15`

Now, `2/15` work is done by X and Y in 1 day.

So, `4/15` work will be done by X and Y in `(15/2 xx 4/5)` = 6 days.

Hence, total time taken = (6 + 4) days = 10 days.