Given: A and S working alone can complete a work in 20 and 30 days respectively Working together, S left the work 5 days before completion. Formula used: The efficiency of a person is the inverse of the time taken Calculation: According to the question: Per day efficiency of A=
1
20
Per day efficiency of S=
1
30
Working together, per day efficiency =
1
20
+
1
30
⇒
(3+2)
60
=
5
60
=
1
12
Let together they worked for d days Then, total work gets completed in d + 5 days ⇒
d
12
+
5
20
=1 ⇒
d
12
=
3
4
⇒ d = 9 Now, d + 5 = 14 ∴ Total work gets completed in 14 days.