Calculate $9 for 3 kg or $12 for 4 kg

Step by step

The question

Question: which is the better buy, A: $9 for 3 kg, or B: $12 for 4 kg?

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

We find the price for 1 kg in each deal.

1 Write both as fractions

We write each deal as a fraction.

The money goes on top.

The kg go on the bottom.

2 Divide to get 1 at the bottom

We want 1 kg on the bottom.

In A, we divide the top and the bottom by 3.

In B, we divide them by 4.

9 divided by 3 is 3.

12 divided by 4 is 3.

So A is 3 dollars per kg.

B is 3 dollars per kg.

3 Compare

Both cost 3 dollars for 1 kg.

So both deals are just as good.

Neither one is better.

Let's look back.

First: write both as fractions.

Then: divide to get 1 at the bottom.

Last: compare.