Multiplying and Dividing Fractions Lesson 2, Topic 3

The Good News The good news about multiplying and dividing fractions is that you never need to find a common denominator as you do when adding or subtracting. Multiplying fractions is similar to multiplying whole numbers. Dividing fractions is a little more work, requiring two steps to get the answer.

Multiplying Fractions If you set the problem up horizontally, all you need to do is multiply across the top and then multiply across the bottom Example: Since this fraction cannot be reduced, you’re done!

Multiplying Fractions by Whole Numbers When multiplying a whole number by a fraction, make the whole number a fraction by putting a 1 under it and them multiple as usual. Example: Reduce to 1 (any fraction with the same numerator and denominator is equal to 1).

Multiplying Mixed Numbers Mixed numbers are whole numbers with fractions, such as 5 ¼. The mixed number must be changed to an improper fraction before multiplying. Do this by multiplying the whole number by the denominator and then add the numerator to that total.

Changing Mixed Numbers Example: 2 2 (whole number) x 12 (denominator) = 24 24 + 1 (numerator) = 25. The bottom number is the same in the new improper fraction, so your improper fraction is

Dividing Fractions Two steps are required to divide fractions. It sounds silly, but to divide fractions, all you actually do is multiply. First, flip the second fraction over so the numerator is now on the bottom. Next, rewrite the problem using the multiplication sign and multiply as usual.

Division Example EXAMPLE: Step 1: Flip the second fraction upside down Step 2: Rewrite the problem using the multiplication sign with the new fraction. Then multiply and reduce if possible.

Other Division Tips If there is a whole number in a division problem, put a 1 under it first to write it as a fraction, then flip the second fraction and multiply. If there are mixed numbers, convert them to improper form first, then flip and multiply.

Summary To multiply fractions, multiply the numerators by each other and the denominators by each other. To divide fractions, flip the second number over and multiply as usual. Put a 1 under a whole number to make it a fraction. Convert mixed numbers to improper fractions before multiplying or dividing.

Next Steps Click Assignment 1 to continue.