SSC CHSL 24 Mar 2018 Shift 2 Paper

Let a man can do 1 unit/day
⇒ Total work = $50\times 28=1400$ man days
So, work done in first 10 days by 50 men = $10\times 50=500$ man days
Then, work done in next 10 days by 40 men = $10\times 40=400$ man days
Similarly, 300 man days after next 10 days and 200 after that.
Thus, $500+400+300+200=1400$ man days
⇒ Total days required = 40 days