Page 35 - Mathematics Coursebook

3.2 Multiplying and dividing by 10, 100 and 1000

Worked example 3.2B

Work out the answer to each of the following: a 32 ÷ 1000 b 47.96 ÷ 10

Solution

a 32 ÷ 1000 = 0.032 Move the digits three places to the right and fi ll the empty spaces with zeros.
b 47.96 ÷ 10 = 4.796 Move the digits one place to the right. There are no empty spaces to fi ll
with zeros.

) Exercise 3.2

1 Work these out.
a 4.6 × 10 b 0.389 × 10 c 2.5 × 100 d 0.07 × 100
e 6.5 × 1000 f 0.0389 × 1000 g 700 ÷ 10 h 4.22 ÷ 10
i 620 ÷ 100 j 43 ÷ 100 k 420 ÷ 1000 l 8.1 ÷ 1000
2 Hannah works out 52 ÷ 10 and 4.6 × 100.
She checks her answers by working backwards. 52 ÷ 10 = 5.2 Check: 5.2 × 10
Work out the answers to these questions. = 52
Check your answers by working backwards. 4.6 × 100 = 4600 Check: 4600 ÷ 100
a 3.7 × 10 b 0.42 × 1000 = 46 x
c 6.7 ÷ 10 d 460 ÷ 100 Correct answer
4.6 × 100 = 460 Check: 460 ÷ 100
3 Which symbol, × or ÷, goes in each box to = 4.6
make the statement correct?
a 45 10 = 4.5 b 3.2 100 = 320
c 0.02 1000 = 20 d 0.3 100 = 0.003
e 560 1000 = 0.56 f 0.09 10 = 0.9

4 Which of 10, 100 or 1000 goes in each box to make the statement correct?
a 3.8 × = 38 b 0.002 × = 0.02 c 0.05 × = 50
d 6.12 × = 6120 e 21 ÷ = 0.21 f 730 ÷ = 7.3
g 56 ÷ = 0.056 h 0.2 ÷ = 0.002 i 0.8 ÷ = 0.08

5 Use the numbers from the box to complete these calculations.
You can only use each number once. You should have no 0.047 8.2 0.04 110 0.3 0.82 300 3.2
numbers left at the end.
a 11 × 10 = b 4 ÷ 100 = c × 100 = 320
d 47 ÷ 1000 = e ÷ 10 = f × 1000 =
6 In a supermarket lemons are sold in bags of 10 for $3.50.
How much does each lemon cost?
7 A builder estimates he needs 1600 nails for a job he is doing.
The nails are sold in boxes of 100. How many boxes does he need?
8 Alexi thinks of a number. He multiplies his number by 10, and
then divides the answer by 100. He then multiplies this answer by 1000

and gets a final answer of 67. What number does Alexi think of first?

34 3 Place value, ordering and rounding