Chapter 7 Decimals Worksheet - New Century Maths Page 12
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38e 929 ÷ 5 ≈ 1000 ÷ 5
= 200
(Actual answer = 185.8)
f 510 ÷ 24 ≈ 500 ÷ 20
≈ 50 ÷ 2
= 25
(Actual answer = 21.25)
2 Now estimate the answers to these:
a 27 + 11 + 87 + 142 + 64
b 55 + 34 − 22 − 46 + 136
c 684 + 903
d 35 + 81 + 110 + 22 + 7
e 517 − 96
f 210 − 38 − 71 + 151 − 49
g 766 − 353
h 367 × 2
83 × 81
j 984 × 16
i
k 828 ÷ 3
507 ÷ 7
l
Adding and subtracting decimals
Careful setting out is essential when adding and subtracting decimal numbers.
When adding or subtracting whole numbers, we must write them under one another in their
correct place-value columns:
67
Not:
67
486
486
9
9
302
302
+ 59
+ 59
923
???
The same is true when adding and subtracting numbers that have decimal points.
Example 11
Add 16.27, 10.92, 4.03, 0.89, 32, 0.6
Solution
Estimate: 16 + 11 + 4 + 1 + 32 + 1 = 65.
The answer should be about 65.
16.27
10.92
4.03
0.89
32.0
Remember that 32 is the same as 32.0 or 32.00.
+ 0.6
64.71
When adding or subtracting decimals, keep decimal points under one another.
209
DECIMALS
CHAPTER 7
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