Free Professional Development

Or

Tutorial

Ratio: comparison of two numbers, usually written as a fraction

Proportion: two ratios set equal to each other

Variable: a symbol, usually a letter, that takes the place of a value

Numerator: the top or left side of a fraction

Denominator: the bottom or right side of a fraction

There are many different ways to solve for a missing number in a proportion. The method we will look at today is turning them into equations. Let's look at this proportion for an example: 3/4 = 6/x. We are looking for the missing value at x.

To do this, we will start by multiplying the first numerator by the second denominator. In this case, my values are 3 and x. 3 time x is 3x.

Now, we will multiply the first denominator by the second numerator. My values are 4 and 6. 4 times 6 is 24.

I will now set these two values equal to each other: 3x = 24.

How do we solve for the x? To find the value of x, we will divide each side of the equation by 3. 3x divided by 3 is just x. 24 divided by 3 is 8.

My answer is x = 8.

If we put 8 back in for x, we will see that our fractions are equal, or proportional.

3/4 = 6/8