mind twister

10 people do the job in 10 hours = the job needs 100 man-hours

15 people do the job in 5 hours = the job needs 75 man-hours

This is contradictory. There is something amiss here. Do give clarification. 

1st case- The portion of work performed by 10 people in 1 hour = 1/10 part of work

2nd case- The portion of work done by 15 people in 1 hour = 1/5 part of work

therefore, 25 people can do the part of work in 1 hour = 1/10 + 1/5 = 3/10 par of work

so, total time taken by 25 people to complete the task = 10/3 hour = 3 hours and 20 min = 200 min

The work will be completed by 3.75 hours i.e. 3 hours and 45 minutes...

3 hours & 20 mins..