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Decimals: Multiplying and Dividing

Decimals: Multiplying and Dividing

Decimals: Multiplying and Dividing

Multiplying and dividing decimals can be achieved in a similar way to regular numbers.

Multiplying and dividing decimals is best achieved by moving the decimal point first.

When multiplying, move the decimal point to the right until both numbers are whole numbers. Then, when you have your answer, move the decimal point to the left by the same amount.

Let's try 2.1×3.42.1 \times 3.4


Change these to whole numbers

2.1×3.421×342.1 \times 3.4 \rightarrow21 \times 34


Multiply these numbers

21×34=71421 \times 34=714


Move the decimal point back

To make whole numbers, we moved the decimal point one place to the right for each number. Now, we need to move it the same amount of places to the left: 7147.14714 \rightarrow7.14


So our answer is 7.147.14

Nice! 👍


Check that this is reasonable

Round your numbers to 22 and 3.43.4. 2×3.4=6.82 \times 3.4=6.8, so our answer of 7.147.14looks like it is in the right area!

Find 1.44×1.21.44 \times 1.2

Find 45.6×3.245.6 \times 3.2

When dividing, we move the decimal points the same number of places to the right for each number and then do the division with whole numbers. We do not need to do anything to the answer.

Let's have a go at 3.150.45\dfrac{3.15}{0.45}


Make the numerator a whole number

This means moving 2 places to the left. 3.153153.15\rightarrow315


Adjust the denominator in the same way

We moved the numerator 2 places, so we should also move the denominator 2 places to the left. 0.45450.45\rightarrow 45


Divide the two whole numbers



Nice! 🙌

The answer is 77 - no need to move the decimal place again. This is because the numerator and denominator stay in the same ratio.

What is 3.40.17\dfrac{3.4}{0.17}?