Which is the better 18 cans of cat food for $15 or 12 cans for $9

18 cans = 15 dollars

18/18 cans = 15/18 dollars divide both sides by 18

1 can = 0.83 dollars

1 can = 83 cents <<--- first deal

12 cans = 9 dollars

12/12 cans = 9/12 dollars ... divide both sides by 12

1 can = 0.75 dollars

1 can = 75 cents <<--- second deal

The first deal costs 83 cents per can.

The second deal costs 75 cents per can.

The second deal is the better offer, since it's cheaper per can