Chapter 7 Decimals Worksheet - New Century Maths Page 18
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382 Given that 23 × 47 = 1081, find:
a 2.3 × 47
b 230 × 4.7
c 23 × 0.47
Solution
Multiplication
Estimate
Answer
23 × 47
1081
(given)
2.3 × 4.7
2 × 5 = 10
a
10.81
use the digits 1081 to make a number near 10
230 × 4.7
200 × 5 = 1000 1081
b
use the digits 1081 to make a number near 1000
23 × 0.47
20 × 0.5 = 10
c
10.81
use the digits 1081 to make a number near 10
Exercise 7-07
Example 13
1 Copy and complete each of the following tables:
a
Multiplication
Estimate
Answer
69 × 18
1242
690 × 180
6.9 × 180
6.9 × 1.8
690 × 1.8
b
Multiplication
Estimate
Answer
104 × 42
4368
10.4 × 42
1.04 × 4.2
104 × 4.2
0.104 × 4.2
c
Multiplication
Estimate
Answer
38 × 92
3496
3.8 × 92
38 × 920
38 × 0.92
380 × 0.92
2 Given that 63 × 34 = 2142, use estimates to find:
a 630 × 340
b 0.63 × 3.4
c 0.63 × 3400
d 3.4 × 630
e 6.3 × 34 000
f 63 × 340
215
DECIMALS
CHAPTER 7
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