Show students that a fraction is made with a numerator and a denominator. To make fractions have a common denominator, you must make sure that the denominators of both fractions are the same. You can do this by multiplying or dividing one or both of the fractions. Show, using
that you can divide by 2 to get
. Or how you can multiply
by 2 to get
. Using the following problem with a fraction bar, check that students can convert
to eighths. Have students repeat this with the next two problems. If you have a fraction which must be converted to a specific denominator, then you divide to reach that denominator. The numerator must also be divisible by that same number. To demonstrate, show
. Explain that you can divide the first and last fractions by 2 to get fourths. The fraction
will have to be divided by 3 to get fourths. So you must also divide the numerator (9) by 3. Use the next problem to check that students are able to change their fractions to fifths and fortieths. Next, explain how students can find a common denominator for 2 fractions without knowing which denominator they must use. Tell students that you can multiply the denominators together to find the denominator you should use. Ask students to solve the following two problems to check their understanding. Students finally drag the fractions to the correct denominators.
Check that students are able to find common denominators by asking teh following questions:
- What are fractions with common denominators?
- How do you make fractions have a common denominator?