year 8 maths

4D
Computation with decimals
219
Example 11 Multiplying and dividing by powers of 10
Calculate:
a 9.753 ÷ 100
b 27.58 × 10 000
SOLUTION
EXPLANATION
a 9.753 ÷ 100 = 0.09753 Dividing by 100 , therefore decimal point appears
to move two places to the left. Additional zeros
are inserted as necessary.
.09.753
b 27.58 × 10000 = 275800
Multiplying by 10000 , therefore decimal
point appears to move four places to the right.
Additional zeros are inserted as necessary.
27.5800.
Example 12
Multiplying decimals
Calculate:
a 2.57 × 3
b 4.13 × 9.6
SOLUTION
a 1
2 2 5 7
× 3
7 7 1
2.57 × 3 = 7.71
b 413
× 96
2478
37170
39648
4.13 × 9.6 = 39.648
EXPLANATION
Perform multiplication ignoring decimal point.
There are two decimal places in the question, so two
decimal places in the answer.
Estimation is less than 10 (≈ 3 × 3 = 9) .
Ignore both decimal points.
Perform routine multiplication.
There is a total of three decimal places in the question,
so there must be three decimal places in the answer.
Estimation is about 40 (≈ 4 × 10 = 40).
Cambridge Maths NSW
Stage 4 Year 8 Second edition
ISBN 978-1-108-46627-1 © Palmer et al. 2018
Cambridge University Press
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