Calculate $12 for 4 pounds or $20 for 5 pounds

Step by step

The question

Question: which is the better buy, A: $12 for 4 pounds, or B: $20 for 5 pounds?

The amounts are different, so we can't just look at the prices.

We find the price for 1 pound in each deal.

1 Write both as fractions

We write each deal as a fraction.

The money goes on top.

The pounds go on the bottom.

2 Divide to get 1 at the bottom

We want 1 pound on the bottom.

In A, we divide the top and the bottom by 4.

In B, we divide them by 5.

12 divided by 4 is 3.

20 divided by 5 is 4.

So A is 3 dollars per pound.

B is 4 dollars per pound.

3 Compare

3 dollars is less than 4 dollars.

Deal A costs less for each pound.

So deal A is the better buy.

Let's look back.

First: write both as fractions.

Then: divide to get 1 at the bottom.

Last: compare.