Multiplying and Dividing Decimals by 10
Multiply and divide decimals by multiples of powers of 10 without a calculator, applying knowledge of place value and proficiency with multiplication facts.
Read this first
The digits move columns. The decimal point stays where it is.
Times 10 moves every digit one column left.
Words you need
- Column
- A place a digit can sit in.
- Multiple of 10
- 10, 100, 1000 and so on.
- Place value
- What a digit is worth.
Worked example
e.g. What is 3.6 x 100?
- Times 100 is two lots of times 10.
- Each digit moves two columns to the left.
- The 3 moves from ones to hundreds. The 6 moves from tenths to tens.
- 3.6 x 100 = 360.
Do not count zeros. Count how many columns the digits move.
Practice
The pictures fade as you go. By the last few you are on your own.
1What is 2.4 x 10?with a picture
Answer24.
2What is 5.7 x 1000?with a picture
Answer5700.
3What is 42 divided by 10?with a hint
Need a hint?
Dividing moves digits right.
Answer4.2.
4What is 6.5 divided by 100?with a hint
Need a hint?
Move two columns right.
Answer0,065.
5What is 0.08 x 100?on your own
Answer8.
6What is 350 divided by 1000?on your own
Answer0.35.
7Why does 'add a zero' fail for 3.6 x 10?on your own
AnswerYou would write 3,60, which is still 3.6.
Think about it
1
Why is 'add a zero' a bad rule for decimals?
One good answerAdding a zero after the point changes nothing.
2
What happens to the place value when you divide by 100?
One good answerEach digit becomes a hundred times smaller.
Common mistakes
Adding a zero to the end.
That only works for whole numbers.
Moving the point instead of the digits.
Either idea works, but pick one and stay with it.