Parimal has done
4
1
​
th of a job in 10 days, Salim completes the rest of the job in 20 days. In how many days can they together do the job?

Parimal completes
4
1
​
of the work in 10 days.
Time taken by Parimal to complete the whole work alone:

T
Parimal
​
=10×4=40 days
Remaining work = 1−
4
1
​
=
4
3
​

Salim completes
4
3
​
of the work in 20 days.
Time taken by Salim to complete the whole work alone:

T
Salim
​
=20×
3
4
​
=
3
80
​
 days
Let total work be 80 units (LCM of 40 and
3
80
​
).

Efficiency of Parimal =
40
80
​
=2 units/day

Efficiency of Salim =
3
80
​

80
​
=3 units/day

Combined efficiency of Parimal and Salim = 2+3=5 units/day.

Time taken by both together to complete the job:

Time=
Combined Efficiency
Total Work
​
=
5
80
​
=16 days