DECIMAL MULTIPLICATION
One notebook
weighs 1.25kg
3 notebooks weigh
1.25 + 1.25 + 1.25 = 3.75kg
1.25 x 3 = 3.75kg
5 notebooks weigh
1.25 + 1.25 + 1.25 + 1.25 + 1.25 =
4.25kg
1.25 x 5 = 4.25
DECIMAL NUMBERS multiply by 10s, 100s, 1000s
When a decimal
number is MULTIPLY by 10,
the decimal value shifts by ONE PLACE to the RIGHT.
the decimal value shifts by ONE PLACE to the RIGHT.
1
“shift” of decimal point to the right is equal to
multiply by 10.
Examples:
Practice
Find (a) 1.5 x 3000
(b) 0.013 x 1000
(c) 2.08 x 10
MULTIPLICATION METHOD
The method to do multiplication
without using addition:
Method
Example:
Example:
132.4 x 0.02
Step1: Multiply without decimal point
1324
x 2 = 2648
Step2: Count number of decimal places
132.4
has 1
0.02 has 2
Total = 3 decimals
Step3: Place decimal places in answer
How to explain the method?
Given Number: 132.4 to multiply by 10 = 1324 {shift 1 to right}
0.02 to multiply by 100 = 2 {shift 2 to right}
1324 x 2 = 2648
Now, we
need to shift 3 places to the left since we shift 3 to right
2648 shift 3 to left = 2.648
DIVISION
DIVIDING DECIMAL NUMBERS BY 10s, 100s, 1000s
When a decimal
number is divided by 10,
the decimal value shifts LEFT by one place.
<Divide by 10 is equal to 1 LEFT shift
decimal point;
100 -> 2 LEFT shifts>
Example
Practice
(1)
24.6 ÷ 1000 (2)
24700 ÷ 10 (3) 38.09 ÷
1000
DIVISION METHODS
Remember: 10/10
= 1
100 / 100 = 1
100 / 100 = 1
Method 1 (Remove all decimal places)
Example
Find
1.86
0.3
Step1: Multiply by multiple of 10 to remove decimal places
1.86 x 100
0.3 x
100
Step2: Do the division
= 186/30
= 62/10
= 6.2
Method 2 (Remove denominator/divisor decimal places)
Find
1.84
0.4
Step1: Multiply denominator by multiple of 10 to remove decimal places
Find
1.84 x10 = 18.4
0.4 x10 4
Step2: Do long division
4.6
4 )18.4
- 16
2.4
- 2.4
0
