Anil alone can do a job in 20 days while Sunil alone can do it in 40 days. Anil starts the job, and after 3 days, Sunil joins him. Again, after a few more days, Bimal joins them and they together finish the job. If Bimal has done 10% of the job, then in how many days was the job done?

Let the total work be 40 units (the LCM of 20 and 40).

The efficiency of Anil $=\frac{40}{20}=2$ units/day.
The efficiency of Sunil unit/day.

Bimal does 10% of the job, which is $10\%\text{of}40=4$ units of work.

The remaining 90% of the job, which is $40-4=36$ units, is completed by Anil and Sunil.

Anil worked from the first day until the job was completed. Let the total number of days taken to finish the job be $d$.

Sunil joined after 3 days, so Sunil worked for $d-3$ days.

Thus, the total work done by Anil and Sunil is:
$2d+1(d-3)=36$

Solving for $d$:
$3d-3=36$
$3d=39$
$d=13$

Therefore, the job was done in 13 days.