Time taken by A to complete the work =x days ∴ Time taken by B to complete the work =3x days ∴‌‌3x−x=2x=40 ⇒‌‌x=20 and 3x=60 ∴(A+B)′ s 1 day's work =‌
1
20
+‌
1
60
=‌
3+1
60
=‌
4
60
=‌
1
15
∴A and B together will complete the work in 15 days.