A can do a work in 15 days and B in 20 days. If they work on it together for 4 days, then the fraction of the work that is left is :

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Question: A can do a work in 15 days and B in 20 days. If they work on it together for 4 days, then the fraction of the work that is left is :
[A].

1
4

[B].

1
10

[C].

7
15

[D].

8
15

Answer: Option D

Explanation:

A’s 1 day’s work = 1 ;
15
B’s 1 day’s work = 1 ;
20
(A + B)’s 1 day’s work = 1 + 1 = 7 .
15 20 60
(A + B)’s 4 day’s work = 7 x 4 = 7 .
60 15
Therefore, Remaining work = 1 – 7 = 8 .
15 15