Let the time taken by B to complete the work, W be n days. ∴ Time taken by A to complete the work, W = (n - 40) days Work done by A in 1 day = 3 × Work done by B in 1 day ∴
W
n−40
=3×
w
n
⇒3n−120=n⇒n=60 Work done by A in 1 day + Work done by B in 1 day =
W
60−40
+
W
60
=
W
20
+
W
60
=
4
60
W=
W
15
∴ Number of days taken by both of them to complete the work =
W
(
W
15
)
=15days Trick: Efficiency of A is 300% and Efficiency of B is 100% 100(x)=300(x−40) ⇒x=60days 100(60)=400d d=15days