Cross Product: Definition, Properties, Rules & Example

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  • 0:02 The Cross Product Method
  • 0:43 Example of the Cross…
  • 1:39 Rules for Comparing Fractions
  • 2:23 Lesson Summary
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Lesson Transcript
Instructor: Misty Dawn James

Misty has a Master's in Educational Leadership and has taught in alternative educational for thirteen years. She is currently working on a Doctoral Degree in Education.

The cross product method is a way to compare two fractions. In this lesson, you'll learn how to perform the cross product method accurately and understand the results in order to identify which fraction is bigger or smaller or if the fractions are equivalent.

The Cross Product Method

The cross product method is used to compare two fractions. It involves multiplying the numerator of one fraction by the denominator of another fraction and then comparing the answers to show whether one fraction is bigger or smaller, or if the two are equivalent. This method is a shortcut to finding a common denominator and doesn't change the value of either of the fractions involved.

We can only compare two fractions at a time with this method, so if you're trying to compare more than two fractions, you'll need to repeat these steps using two fractions at a time. Let's look at a step-by-step example to see just how easy the cross product method can be.

Example of the Cross Product Method

Step One:

Write the fractions vertically, next to each other. Be sure to leave a space in between them, like this:

step 1

Step Two:

Draw an 'X' diagonally between the two fractions. This helps remind you which numbers to multiply with each other:

step 2

Step Three:

Multiply the numerator and denominator that each line of the 'X' connects. Be sure to write your products down in such a way that you can identify which fraction they each represent. This is where mistakes tend to happen.

step 3

Step Four: Compare the Products

After you multiply the numerator 1 of the fraction 1/2 and the denominator 5 from 3/5, the product 5 is smaller than the product you get from multiplying the denominator 2 of 1/2 and the numerator 3 of 3/5. You'll see that the product 6 is larger than the product of 5, so 3/5 is larger than 1/2.

step 4

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