SOLUTION: Hi, This is for a 7th math project on finding real life applications of algebra. I already used your equation for finding the full price of a car that was 20% off and only gave t

Question 930187: Hi,
This is for a 7th math project on finding real life applications of algebra. I already used your equation for finding the full price of a car that was 20% off and only gave the sale price. I applied it to another sale item. Thanks! My question is if I have 4 cereals all on sale for $2.50 each and they are all different sizes 12oz, 11.5oz, 13.5oz and 12.25oz. Is there a way to tell which is the best deal. I know if I divide the cost by ounces I can see which one cost less per ounce (the larger size being the best deal) but is there an algebraic equation that can prove this as well?
If you can answer this i would really appreciate the help.
Thanks:)
Answer by richard1234(7193) (Show Source): You can put this solution on YOUR website!
If they are all the same price, then clearly the larger size has the cheaper unit price. A completely algebraic solution is unnecessary, but do note that the unit price per oz is

where x is the number of ounces, and this quantity is strictly decreasing in x, so a larger x implies smaller unit price.
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