Let's say you had two boxes of cereal labeled A and B. Also let's come up with a hypothetical situation that...
- box A costs $2 and weighs 10 ounces
- box B costs $3 and weighs 20 ounces
The question is: which is the better deal? By that I mean which is cheaper per ounce.
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For box A, we have this ratio
2 dollars : 10 ounces
If we divide both sides by 10, then we end up with
2/10 dollars : 10/10 ounces
0.20 dollars : 1 ounce
20 cents : 1 ounce
This tells us that the unit rate for box A is 20 cents per ounce. In other words, 1 ounce costs 20 cents or each ounce costs 20 cents.
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Do a similar thing for box B
3 dollars : 20 ounces
3/20 dollars : 20/20 ounces
0.15 dollars : 1 ounce
15 cents : 1 ounce
So box B costs 15 cents per ounce
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In summary,
Box A's unit rate is 20 cents per ounce
Box B's unit rate is 15 cents per ounce
Box B is the better deal since it's 5 cents cheaper per ounce.
