Question

15 men can do a piece of work in 210 days but at the end of every 10 days 15 additional men are employee in how many days will it be finished

Answer 1

15 men do 1 work in 210 days

So 15 men will do 1/210th work in 1 day

So "1 man will do 1/3150th work in 1 day"<----use this as your main statement

Now lets start , keeping in mind the base statement,

First 10 days there are 15 men working so the work completed will be 1/3150*10 days*15 men=1/21

Next 10 days there are 30 men working so the work completed will be 1/3150*10 days*30 men=2/21

Next 10 days there are 45 men working so the work completed will be 1/3150*10 days*45 men=3/21 (or 1/7)

This will continue as 4/21,5/21 and so on...

If you notice when you reach 6/21 and add all the work, it will be 21/21 = 1 which means the work has completed.

That means the number of days to complete the work would be 10+10+10+10+10+10= 60 days.

So the answer is 60 days!