40 men can complete a work in 15 days. Three days after they started working, 20 more men joined them. In how many days the total work will be completed?

11

40 men complete the work in 15 days

In 3 days, $\frac{1}{5}$ of the work is complete 

20 more men join, 

time taken to complete the remaining  work, 

using the following formula 

$\frac{Men\; \times\; Days}{Work}$ = Constant 

$\frac{40\; \times\; 15}{5}$ = $\frac{60\; \times\; days}{4}$

No. of days = 8

Total time taken to complete the work = 8 + 3 = 11 days