Multiplying Decimals
Multiplying Decimals
http://www.mathsisfun.com/multiplying-decimals.html
8.17.2011
Multiply
without the decimal point, then re-insert it in the
correct spot!
How to Multiply
Decimals
Just follow these steps:
- Multiply
normally, ignoring the decimal points.
- Then put the decimal
point in the answer - it will have as many decimal places as the two
original numbers combined.
In other words, just count
up how many numbers are after the decimal point in both numbers
you are multiplying, then the answer should have that
many numbers after its decimal point.
Example: Multiply 0.03 by 1.1
|
start
with: |
|
0.03 × 1.1 |
|
multiply
without decimal points: |
|
3 × 11 = 33 |
|
0.03
has 2 decimal places, |
|
0.033 |
|
|
See the Multiplying Decimals
Animations |
How
Does It Work?
Because when you multiply
without the decimal point, you are really shifting the decimal point to the
right toget it out of the way:
|
Original: |
1
Move: |
2
Moves: |
3
Moves: |
|||
|
0.03
× 1.1 |
|
0.3 × 1.1 |
|
3. × 1.1 |
|
3. × 11. |
Then we do the (now easy) multiplication:
3. ×
11. = 33.
But remember, we did 3
Moves of the decimal point, so we need to undo that:
|
3
Moves: |
2
Moves: |
1
Move: |
Correct |
|||
|
33. |
|
3.3 |
|
0.33 |
|
0.033 |
Here are some more
examples:
Example: Multiply 0.25 by 0.2
|
|
start
with: |
|
0.25 × 0.2 |
|
|
multiply
without decimal points: |
|
25 × 2 = 50 |
|
|
0.25
has 2 decimal places, |
|
0.050 |
Example: Multiply 102 by 0.22
|
|
start
with: |
|
102 × 0.22 |
|
|
multiply
without decimal points: |
|
102 × 22 = 2,244 |
|
|
102
has 0 decimal places, |
|
22.44 |
Common
Sense
As a final check you can
put your "common sense" hat on and think "is that the right size?", because
you don't want to pay ten times too much for anything, nor get only one-tenth
of what you need!
And that's all.
Just
remember: the answer should have the same number of decimal places as are in
both the numbers you are multiplying.
Decimal
Worksheets
Quiz: Question 1 Question 2 Question 3 Question 4 Question 5Question 6