Chain Rule - General Questions

25 men working 8 hours a day can complete a work in 24 days. In how many days can 20 men working 6 hours a day complete the same work?

If 18 pens cost Rs. 2340, how much do 22 pens cost?

If 7 pens cost Rs. 490, how much do 20 pens cost?

If 19 pens cost Rs. 1235, how much do 22 pens cost?

If 6 pens cost Rs. 960, how much do 26 pens cost?