Equivalent Fractions: Creating Common Denominators

GOAL: You will learn how to create common denominators between fractions.

GOAL: You will learn how to create common denominators between fractions. HOW: You will use equations to create common denominators.

1 2 You know that fractions can be shown as part of a whole, part of a set, or on a number line as a value between zero and one. You know that the top number in a fraction is called a numerator and stands for the part of the whole. (draw 1) You also know that the number down below the line is the denominator and that represents all the parts that make up the whole. (draw 4) You know that the word equivalent means equal. When we talk about common denominators that means that the denominators of the fractions will be the same.

Least Common Multiples of 6  When finding common denominators, you first need to know about least common multiples. Multiples are the products of the number and the numbers 1, 2, 3, 4, 5 – or, in other words, the answer you get when you multiply your first number by the numbers 1, 2, 3, 4, 5 The least common multiple is the smallest multiple that both the numbers share. Let’s take a look at how we use least common multiples when finding common denominators for fractions. Let’s take a look at the fractions 2/3 and 2/5.

First we are only going to focus on the denominators (highlight) – that’s the part of the fraction that we need to make sure is equal, so those two numbers – 3 and 5 – are the numbers we need to find the least common multiple for. Here are the multiples of 3 (show chart – 1x3 = 3, 2x3 = 6 etc)

Here are the multiples of 5 (show chart) The least common multiple between the two is 15 (highlight on the chart) So, you probably remember that whatever we do to the denominator, we have to do to the numerator. In the fraction 2/3 if we multiply 3 x 5 = 15, we need to multiply 2 x 5 - 10. Our new fraction is 10/15 In the fraction 2/5, if we multiply 5 x 3 = 15, we need to multiply 2 x 3 = 6. Our new fraction is 6/15. Finding common denominators is important when you are adding fractions together or putting fractions in order from least to greatest or greatest to least.

Here are the multiples of 5 (show chart) The least common multiple between the two is 15 (highlight on the chart) So, you probably remember that whatever we do to the denominator, we have to do to the numerator. Let’s take a look at how we can make these denominators equivalent. In the fraction 2/3 if we multiply 3 x 5 = 15, we need to multiply 2 x 5 - 10. Our new fraction is 10/15 In the fraction 2/5, if we multiply 5 x 3 = 15, we need to multiply 2 x 3 = 6. Our new fraction is 6/15. Finding common denominators is important when you are adding fractions together or putting fractions in order from least to greatest or greatest to least.

In the fraction 2/5, if we multiply 5 x 3 = 15, we need to multiply 2 x 3 = 6. Our new fraction is 6/15. In the fraction 2/3 if we multiply 3 x 5 = 15, we need to multiply 2 x 5 - 10. Our new fraction is 10/15 Finding common denominators is important when you are adding fractions together or putting fractions in order from least to greatest or greatest to least.

In this lesson, you learned how to create common denominators by using equations.