1.2 Multiplying decimals

1.2 Multiplying decimals

Hello grade 7!

How to Multiply Decimals

Just follow these steps:

1. Multiply normally, ignoring the decimal points.

2. Then put the decimal point in the answer - it will have as many decimal places as the two original numbers combined.

In other words...

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Your answer should have the same number of decimal places as the numbers in the question!

Read this example carefully ----->

Watch the two animations on the next slide to see how this works...

(You can click 'play' on the animations - scroll down a bit to see the second one)

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Example 1: Using written multiplication, work out 120.3 x 19

Step 1

Multiply as usual, ignoring the decimals

Step 2

Count the number of digits after the decimal point in both numbers in the question -----> here there is one

Put the decimal point into your answer so that it also has only one decimal place

so... 120.3 x 19 = 2285.7

Notice, there is one decimal place in the answer (and one decimal place in the numbers in the question!)

Example: 3.24 x 0.87

1. Multiply the numbers ignoring the decimal places

2. Position the decimal place in your answer so that it has the same number of decimal places as the numbers in the question

so... 3.24 x 0.87 = 2.8188

Notice, there are four decimal places in the numbers in the question, and four decimal places in the answer!

Now get your paper and a pen/pencil ready

Its your turn!

Multiple Choice

What is 4.82 x 3? Use written multiplication to find your answer.

• 14.46

• 144.6

• 1.446

Multiple Choice

What is 8.28 x 17? Use written multiplication to find your answer.

• 145.76

• 1407.6

• 140.76

Multiple Choice

What is 0.16 x 6.2? Use written multiplication to find your answer.

• 0.993

• 0.992

• 9.992

Multiple Select

How many decimal places would the answer to 5.678 x 9.7765 have?

• seven

• six

• five

• four

Example: Caley works 7.5 hours a day, 5 days a week. How many hours will she work in a week?

Caley will work 7.5 x 5 hours per week

7.5

x 5

----

37.5

----

We need to insert the decimal into the answer so that there is one number after the decimal...

Therefore Caley works 37.5 hours per week

Multiple Choice

If Caley works 37.5 hours a week, how many hours will she work in a year? (hint: there are 52 weeks in a year)

Use written multiplication to find your answer.

• 195

• 1930

• 1950

• 193

Well done :)

You are done for today! Please make sure you've completed the homework quiz which was assigned on Friday

See Google Classroom...