In today’s post we are going to work on **proportions**. This time we will look at a way of solving direct and inverse proportions: **the rule of 3**.

#### What is the rule of 3?

The **rule of 3** is an operation that helps us quickly solve both direct and inverse** proportion** word problems.

In order to use the rule of 3, we need **three values; **two that are proportional to one another, and a third. From there, we will **figure out the fourth value**.

#### Direct rule of 3

We will begin by looking at how to apply it **in the case of direct proportions**.

We will place the **3 values** (which we will call **“a”**, **“b”**, and **“c”**) and the unknown value that we want to figure out (**“x”**) in a table. Next, we will apply the following formula:

We are going to solve the following problem as an example:

*Upon arriving at the hotel, the staff gave us a map displaying the places of interest in the city, and told us that 5 centimeters on the map represented 600 meters in reality. Today we want to go to a park that is located 8 centimeters from the hotel on the map. How far from the hotel is the park?*

Let’s **make a table** with the 3 values and the unknown value (“x”), and we will find “x” **with the formula** that we have just learned.

__Centimeters on the map__ __Meters in reality__

** **

Answer: **The park is located 960 meters from the hotel**

#### Inverse Rule of 3

Now we will look at how to apply the rule of 3 **in the case of inverse proportions**.

We will place the 3 values and the unknown value in the *table, just as we did** in the previous case, b*ut **we will apply a different formula:**

*Let’s look an example:*

*Yesterday, 2 trucks transported goods from the port to the warehouse. Today, 3 trucks, the same size as yesterday, will have to make 6 trips to transport the same amount of goods from the warehouse to the mall. How many trips did the trucks make yesterday?*

We place **the values** in a table and **apply the formula **for the **inverse rule of 3**:

** Trucks Trips Necessary**

* *

Answer: **Yesterday, 2 trucks made 9 trips each**

What did you think of this post? Isn’t it easy to apply the rule of 3 to proportion word problems!

Remember that you will be able to practice **exercises, proportion word problems** and **much more with Smartick!**

### Learn More:

- Direct and Inverse Rule of Three Problems
- Do you Want to Learn Multiplication Tables Tricks?
- How to solve addition problems
- Ratio and Proportion: Concept and Some Examples
- Adding With an Unknown Quantity

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