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Multiplication of Whole Numbers by Fractions

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Multiplication of Whole Numbers by Fractions

Remember Julie and the rainforest dilemma from the Multiplication of Fractions by Whole Numbers Concept? Well, in that problem Julie began by looking at the fraction of rainfall. Then she multiplied that fraction by the number of days.

What if we worked the other way around?

We could do it that way too. We could start with the number of days in the week and multiply the number of days, a whole number, by the fraction of rainfall.

To do this, you will need to know how to multiply whole numbers with fractions. This Concept will teach you how to do this.

Guidance

Previously we worked multiplying fractions by whole numbers, now we can also reverse the order too and multiply whole numbers by fractions.

9 \times \frac{1}{3}

To work through this problem we do the same thing that we did when the numbers were reversed. We can turn 9 into a fraction over one and multiply across.

\frac{9}{1} \times \frac{1}{3} = \frac{9}{3}

Here we have an improper fraction. We can turn this into a mixed number, or in this case a whole number. Nine divided by three is three.

Our answer is 3.

Try a few of these on your own. Be sure to simplify your answer.

Example A

6 \times \frac{1}{3} = \underline{\;\;\;\;\;\;\;}

Solution:  2

Example B

8 \times \frac{1}{2} = \underline{\;\;\;\;\;\;\;}

Solution:  4

Example C

10 \times \frac{1}{2} = \underline{\;\;\;\;\;\;\;}

Solution:  5

Now let's think about the rainforest problem.

Today, Julie is working on the part of the project that has to do with rainfall. The rainforest gets an average of \frac{1}{8}'' of rain each day. Some days there isn’t any rain, but most days there is some. The \frac{1}{8}'' average seems to make the most sense.

Imagine that Julie wants to figure out how much rainfall there will be in 30 days. This is the whole number that she will multiply with the amount of rainfall in one day.

We can multiply 30 times \frac{1}{8}'' to get the total inches of rain.

30 \times \frac{1}{8} = \underline{\;\;\;\;\;\;\;}

Now we multiply just as we would any whole number and fraction.

 \frac{30}{8} = 3 \frac{6}{8} = 3 \frac{3}{4}

This is our answer in simplest form.

Vocabulary

Multiplication
a shortcut for repeated addition
“of”
means multiply in a word problem
Product
the answer to a multiplication problem
Estimate
to find a reasonable answer that is not exact but is close to the actual answer.

Guided Practice

Here is one for you to try on your own.

6 \times \frac{2}{3} = \underline{\;\;\;\;\;\;\;}

Answer

Here we multiply the whole number and the fraction.

 \frac{12}{3} = 4

This is our answer in simplest form.

Video Review

Multiplying Fractions and Whole Numbers

Practice

Directions: Multiply the following fractions and whole numbers. Be sure that your answer is in simplest form.

1. 9 \times \frac{2}{3} = \underline{\;\;\;\;\;\;\;}

2. 6 \times \frac{2}{3} = \underline{\;\;\;\;\;\;\;}

3. 5 \times \frac{2}{5} = \underline{\;\;\;\;\;\;\;}

4. \frac{1}{2} \times 9 = \underline{\;\;\;\;\;\;\;}

5. \frac{2}{7} \times 9 = \underline{\;\;\;\;\;\;\;}

6. \frac{1}{3} \times 7 = \underline{\;\;\;\;\;\;\;}

7. \frac{3}{4} \times 10 = \underline{\;\;\;\;\;\;\;}

8. \frac{3}{4} \times 12 = \underline{\;\;\;\;\;\;\;}

9. \frac{3}{5} \times 10 = \underline{\;\;\;\;\;\;\;}

10. \frac{1}{9} \times 36 = \underline{\;\;\;\;\;\;\;}

11. \frac{1}{9} \times 63 = \underline{\;\;\;\;\;\;\;}

12. \frac{1}{2} \ of \ 14 = \underline{\;\;\;\;\;\;\;}

13. \frac{1}{2} \ of \ 24 = \underline{\;\;\;\;\;\;\;}

14. \frac{1}{4} \ of \ 44 = \underline{\;\;\;\;\;\;\;}

15. \frac{1}{5} \ of \ 35 = \underline{\;\;\;\;\;\;\;}

16. \frac{1}{8} \ of \ 40 = \underline{\;\;\;\;\;\;\;}

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