Ratio

Just as we read in English, mathematics is also read from left to right. So,

we combine the written words according to their order of appearance and convert them into numbers from left to right.

Let's see an example:

The ratio of purple balls to green balls is: $3:2$

Since the first written word is "purple," it represents the first number on the left

We can really see that, for every $3$ purple balls there are $2$ green balls.

Important

Ratios can also be expressed through fractions: $\frac{3}{2}$

and, in such case, we read it from top to bottom.

Another example:

The ratio of pens to markers in Ariel's school case is $2:1$.

Which number refers to pens and which number to markers?

Also, which of the two do we have more of in Ariel's school case?

Solution:

Let's observe the phrase, the ratio of pens to markers in Ariel's school case is

The word that appears first is pens.

Therefore, when reading the ratio, we will relate the first number to the term pens.

That is, the $2$ refers to the pens and the $1$ to the markers.

The ratio expresses that, for every $2$ pens found in the case there is one marker.

So, in general, in Ariel's school case there are more pens than markers. (double)

In Ariel's school case there can be:

$4$ pens, $2$ markers

$8$ pens, $4$ markers

and so on.

The ratio always remains as long as the relationship between pens and markers is $2:1$.

We can encounter the ratio of an object to the entire set.

For example, the ratio of apples to all other fruits in the fridge is $3:5$

This means that out of the $5$ fruits in the fridge, $3$ of them are apples.

We know that the ratio between apples and oranges in a basket is $2:3$. The total amount of fruit in the basket is $25$.
We are asked to calculate the number of apples and oranges in the basket.
We can deduce that the $2$ represents the number of apples and the $3$ represents the number of oranges.
We will denote both fruits with a variable $X$.

Now let's draw a simple equation:

$2X+3X=25$

$5X=25$

$X=5$

From here we can infer that the number of apples is $10 (2X)$ and the number of oranges is $15 (3X)$.
We can always go back and check our result by verifying that the total number of apples and oranges is $25$, as shown in the first piece of data we received.

In the dishware cabinet, there is a total of $30$ utensils that include plates and bowls. The ratio between plates and bowls is $7:3$. 

We are asked to determine how many plates and bowls are in the cabinet.

According to what we have learned, we can deduce that the $7$ represents the number of plates and the $3$ the number of bowls.

Let's denote both with a variable $X$.

Now let's set up a simple equation:

$7X+3X=30$

$10X=30$

$X=3$

From here we can infer that the number of plates is $21 (7X)$ and the number of bowls is $9 (3X)$.

We can always go back and check our result by verifying that the total number of utensils in the cabinet is $30$, as seen in the first given data.