Word Problems: Ratios

When we solve word problems, we often encounter ratios. Whether we're aware of it or not, our universe contains many ratios -- including the so-called "golden ratio" that is so common in nature. When we understand how ratios work, it's easy to solve all kinds of real-world problems. Let's get started:

What is a ratio?

A ratio is a comparison of two different values with the same units. We write these with colons. Here are a few examples: 5:1, 12:30, 1:2

The colon simply means "to," so "5:1" means a "five to one" ratio.

Using our knowledge of ratios to solve word problems

Let's use our knowledge of ratios to tackle a few word problems:

Let's say we have 12 sunfish and 30 rainbow shiners in our backyard pond. What is the ratio of sunfish to rainbow shiners in its simplest form?

We can write the ratio 12:30 as the fraction $\frac{12}{30}$ . Next, we can reduce this fraction to 2/5. Finally, we rewrite it as the ratio 2:5. We also know that the reverse is true, as the ratio of rainbow shiners to sunfish is 5:2.

Now let's say we have a classroom of 32 students with 20 girls. What is the ratio of boys to girls?

We know that the total is 32 -- but we can't make the mistake of giving 20/32 as our answer. This gives us the ratio of girls to the total number of students -- but it doesn't give us the ratio of girls to boys. To find the correct answer, we need the total number of boys.

$30-18=12$ boys

Therefore, the ratio of girls to boys is 20:12 or 5:3 in simplified terms.

Now let's say we're baking a cake using a recipe that calls for a butter-to-sugar ratio of 2:3. If we use 6 cups of butter, how many cups of sugar should we use?

We know that we're using three times as much butter as the original recipe (since 6 is three times 2), so all we need to do is multiply the original sugar amount by three as well.

$3\times 3=9$ cups of sugar.

So, if we use 6 cups of butter, we should use 9 cups of sugar to maintain the 2:3 butter-to-sugar ratio.

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