75.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?
A. 6 days
B. 10 days
C. 15 days
D. 20 days
Answer:
Option : B
Work done by X in 4 days =
|
|
1
|
x 4
|
|
=
|
1
|
20
|
5
|
Remaining work =
|
|
1 -
|
1
|
|
=
|
4
|
5
|
5
|
(X + Y)'s 1 day's work =
|
|
1
|
+
|
1
|
|
=
|
8
|
=
|
2
|
20
|
12
|
60
|
15
|
Now,
|
2
|
work is done by X and Y in 1 day.
|
5
|
So,
|
4
|
work will be done by X and Y in
|
|
15
|
x
|
4
|
|
= 6 days.
|
5
|
2
|
5
|
Hence, total time taken = (6 + 4) days = 10 days.
| |
|
