year 8 maths

4D
Computation with decimals
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4D Computation with decimals
REVISION
This section reviews the different techniques involved in adding, subtracting, multiplying and dividing
decimals.
Reminder:
3.6 ÷ 2 = 1.8
dividend divisor quotient
Let’s start: Match the phrases
There are eight different sentence beginnings and eight different sentence endings below. Your task is to
match each sentence beginning with its correct ending. When you have done this, write the eight correct
sentences in your workbook.
Sentence beginnings
When adding or subtracting decimals
When multiplying decimals
When multiplying decimals by 100
When dividing decimals by decimals
When multiplying decimals
When dividing by 100
When dividing decimals by a whole number
Sentence endings
the decimal point appears to move two places to the right.
the decimal point in the quotient goes directly above the
decimal point in the dividend.
make sure you line up the decimal points.
the number of decimal places in the question must equal
the number of decimal places in the answer.
the decimal point appears to move two places to the left.
start by ignoring the decimal points.
we start by changing the question so that the divisor is a
whole number.
■ Adding and subtracting decimals
• Ensure digits are correctly aligned in similar place value columns.
• Ensure the decimal points are lined up directly under one another.
37.56 + 5.231
37.560
+ 5.231 ✓
37.56
5.231
×
Key ideas
■ Multiplying and dividing decimals by powers of 10
• When multiplying, the decimal point appears to move to the right the same number of
places as there are zeros in the multiplier.
13.753 × 100 = 1375.3 13.753
Multiply by 10 twice.
• When dividing, the decimal point appears to move to the left the same number of places as
there are zeros in the divisor.
586.92 ÷ 10 = 58.692 586.92
Divide by 10 once.
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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