Why does cross simplifying work

You can see this in the examples below or you can scroll down for a video example. Notice that the answer was already simplified and that even though the denominators were not the same, you could still just multiply across. In the next example, we will also use that rule, but the answer has to be simplified. Because of this, we can cross cancel before we multiply. This is much easier! It even works when the fractions are a bit more complicated, as in the example below where we are finding:.

Lastly, simplify 5 and 5, leaving 1 and 1. Multiply three fractions. Simplify before multiplying. Draw a bar model for this situation. Calculate how much he uses for groceries. Jack did all of the simplifying before multiplying. Tina simplified after multiplying. Both of them got the right answer. Simplifying before multiplying does NOT change the final answer—it just makes it easier to multiply because the numbers are smaller!

A self-teaching worktext that teaches fractions using visual models, a sequel to Math Mammoth Fractions 1. The book covers simplifying fractions, multiplication and division of fractions and mixed numbers, converting fractions to decimals, and ratios. See more topical Math Mammoth books. Simplify fractions before multiplying them - a free lesson for 5th grade In this 5th grade lesson, I explain how to simplify fractions before multiplying them. A new notation We will start using a new way to indicate simplifying fractions.

Why are we allowed to simplify in such a manner? Math Mammoth Fractions 2. Math Lessons menu. Hint: it has to do with a "recipe" that many math lessons follow. The do's and don'ts of teaching problem solving in math Advice on how you can teach problem solving in elementary, middle, and high school math.

This does not affect the process at all. Cross multiply as normal. Cross multiplying fractions to determine if one is greater than the other works because it is a shortcut for converting the fractions to a common denominator and comparing fractions. No, you cannot cross multiply when adding fractions.

Cross multiply only when you need to determine if one fraction is greater than another, or if you are trying to find a missing numerator or denominator in equivalent fractions. Cross multiply fractions with variables by multiplying opposite numerators and denominators of equivalent fractions, setting the values equal to one another, and solving for the variable.

Cross multiplication can be used to answer this question. First, multiply 17 by To solve this problem, start by cross multiplying. A man has a garden that is 6 feet wide and 9 feet long. He is planning on increasing the width to 9 feet. If he wants to increase the length proportionally, what would be the new length? To solve this problem, first set up proportional fractions. Study Guides Flashcards Online Courses.

Cross Multiplying Fractions. When cross multiplying fractions, the name sort of hints at how this is actually done. Frequently Asked Questions Q How do you cross multiply fractions? A Cross multiply fractions by multiplying the denominator of one fraction with the numerator of the other fraction and then comparing the two values.