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1. October 4, 2012
Negative numbers and decimals
2. Multiplying and dividing decimals
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2. Explanation October 4, 2012
e
n
s
When you multiply a decimal by
10, or a multiple of 10, the digits
s h de dn uh
t r
all move to the left, according to
how many “0”s there are.
thousandths
s de dnuh
s eno
s h ne
t t
The decimal point stays put. ×× 10
÷100 0 6 6 1
r
When dividing by a multiple of × 10 ÷ 2
0 0 9
10, each digit moves to the
right, according to how many
“0”s there are. If the digits all move beyond the decimal
point, you must write a zero in the “ones” column.
As it is easier, we actually move just the decimal point,
but remember that this represents moving all the digits
the other way.
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3. Practise October 4, 2012
3.92 × 100 392
22.4 ÷ 100 0.224
0.83 × 10 8.3
14.7 ÷ 10 1.47
0.02 × 1000 20
8,390 ÷ 1000 8.39
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4. Explanation October 4, 2012
Multiplying two decimal numbers.
First, ignore the decimal points. 3.24 × 2.3
Multiply. 3.24 × 2.3 = 7452
Count and total the number of
digits after both decimal points, 2
1
3
in the original calculation.
The decimal point should have
this number of digits after it, in 7452
.
you answer.
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5. Practise October 4, 2012
3.92 × 2.2 8.624
22.4 × 1.37 30.688
0.83 × 2.96 2.4568
14.7 × 3.745 55.0515
0.02 × 16.8 0.336
11.66 × 4.853 56.58598
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6. Explanation October 4, 2012
Dividing two decimal numbers.
First, write the division as a fraction. 3.24 ÷ 2.4
Multiply both the denominator and the 3.24
numerator by 10, or 100 or any other 2.4
power of 10, so that the denominator
is a whole number.
If you can, cancel , then divide as normal.
1.35
8 12
24 32.4 0
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7. Practise October 4, 2012
3.12 ÷ 2.4 1.3
7.02 ÷ 1.3 5.4
2.728 ÷ 0.88 3.1
23.836 ÷ 5.7 4.18
0.03 ÷ 0.025 8.5
114.75 ÷ 4.25 27
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End