2E Adding and subtracting decimals Learning intentions
Inter-year links
✔ I can add and subtract positive and negative decimals.
SA LE
Years 5/6 Adding and subtracting decimals Year 7 4C Adding and subtracting decimals
Adding and subtracting decimals
R
Question 3.12 + 4.2
Diagram
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•
-N
O
T
•
Decimals can be added or subtracted in the same way as whole numbers using the vertical 3.02 4.15 algorithm. Add or subtract digits in each column from right to left. + _ 7.17 ➝ Make sure that the decimal points are aligned and the digits are in the correct place values. _ When dealing with negative decimals: ➝ consider the direction of both numbers on the number line, • if they have the same direction, find the sum • if they have different directions, find the difference ➝ consider if the result will be positive or negative. • the sum will have the same sign as the calculation + ( + ) = + • the difference will be positive if the positive number is larger − ( + ) = − • the difference will be negative if the negative number is larger + ( − ) = − − ( − ) = + Simplify the calculation by considering the operation and the sign applied to each decimal.
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+3.12
–1 0
2
3
4 sum
–4.2
5
6
7
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–8 –7 –6 –5 –4 –3 –2 –1 0 sum
–3.12 + 4.2
–2
–1
0
1
Calculation 3.12 + _ 4.20 7.32 _
Result Positive result of 7.32
3. 12 + 4.20 − _ (_ ) 7.32
Negative result of − 7.32
1 10
4.2 0 − 3.1 2 _ _ 1.0 8
Positive result of 1.08
D
difference
3.12 − 4.2
Difference in the negative direction
–4.2 +3.12 –2
1
Sum in the negative direction
Difference in the positive direction
+4.2 –3.12
–3
8
–3.12
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–3.12 – 4.2
1
+4.2
Conclusion Sum in the positive direction
–1
0
1
2
3
4
1 10 Negative result 4.2 0 3.1 2 _ −− − of − 1.08 _ ( _ 1.0 8 ) _
difference
CHAPTER 2 Fractions and decimals — 81 No part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means.
OXFORD UNIVERSITY PRESS
BOOK_OM_VIC_Y8_SB_29235_TXT_PPS_NG.indb 81
21-Oct-21 18:12:00
