In a small machine shop, eight 5-gallon drums of oil are on hand. if 2 gallons are used each day and the owner wants a 30-day supply on hand, how many drums should be ordered?

If 2 gallons of oil are used a day, than he will need 60 gallons of oil, because 30x2=60. For 60 gallons of oil, you would have to have 12 drums because 60÷5=12. Because there is already 8 drums of oil, there would already be 40 gallons because 8x5=40. If the owner already had 40 gallons of oil, they would only have to get 20 more gallons because 60-40=20. That would be 4 drums because 20÷5=4. The owner would have to order 4 more drums of oil.