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Introduction
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In this worksheet, multiply decimal numbers by whole numbers.
- The first stage is to adjust the question so that there are no decimal numbers.
- The second stage is to carry out the multiplication of the whole numbers.
- In the third stage, we adjust the answer back to how it should be with decimals.
Example 1
Multiply
7.8 × 7
Answer
Stage 1
Adjust 7.8 so it becomes a whole number.
We do this by multiplying it by 10 to get rid of the decimal place.
7.8 × 10 = 78
This will mean that our answer will now be 10 times too big. But that is fine!
Stage 2
Now we work out 78 × 7.
Stage 3
Now, remember that this is 10 times too big.
So we divide 546 ÷ 10 = 54.6.
7.8 × 7 = 54.6
Example 2
Multiply
3.68 × 5
Answer
Stage 1
Adjust 3.68 so it becomes a whole number.
We do this by multiplying it by 100 to get rid of the 2 decimal places.
3.68 × 100 = 368
This will mean that our answer will now be 100 times too big. But that is fine!
Stage 2
Now we work out 368 × 5.
Stage 3
Now, remember that this is 100 times too big.
So we divide 1840 ÷ 100 = 18.40 = 18.4.
3.68 × 5 = 18.4
Question
/ 10Mr Shepherd
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Teacher explanation