Using Proportions to Solve Word Problems

Thursday, January 7, 2016

In this video you will learn how to set up proportions in order to solve word problems.

How do you set a proportion?
First will set it up as two fractions that are equal to each other.
The fraction needs to have the same unit on the top and the matching unit on the bottom.
Next, you solve it by cross multiplying.
Finally, you just solve the equation.

Let’s look at an example of setting up a proportion.
Example problem number 1.
A map scale says 1 inch = 2 miles, how many miles will 4 1/2 inches.

Step 1. Set up a proportion of 1 inch =2 miles the
We will set up 1 inch/ 2miles = 4.5 inches/x miles

Step 2. Complete a cross product

Step 3. Solve

Proportion word problem 2

The Ford F150 can travel 150 miles on 10 gallons of gas. How much gas is required to travel 150 miles?

Set up a proportion
150 miles / 10 gallons = 750 miles / x gallons of gas

Now we just complete a cross product.
150 times x = 10 times 750
750 x 10 =7500 and divide both sides of the equation by 150 which equals 50

What does 50 represent?
It represents the gallons of gas.

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