Fifteen men can complete a piece of work in 10 days, working 8 hours per day. How many persons are required to complete double the work in 25 days, working 6 hours per day ?

If 25 men can do a piece of work in 36 days working 10 hours a day, then how many men are required to complete the work working 6 hours a day in 20 days?

12 men can complete a work in 30 days by working 9 hours a day. What is the number of men required to complete 10 times of this work in 24 days by working 5 hours a day ?

7 men can complete a plece of work in 12 days. How many additional men will be required to complete double the work in 8 days ?

90 men can complete a work in 24 days working 8 hours a day. How many men are working 8 hours a day. How many men are required to complete the same work in 18 days working 7(1)/(2) hours a day ?