DECIMALS

1
Decimals are my thing You see them all
around Temperature, time, receipts and
bills They're even in the pound! Can you think
of any more examples?
2
DECIMALS
DECIMALS
3
PLACE VALUE
Hundreds 100s Tens 10s Units 1s . Tenths 10ths Hundredths 100ths Thousandths 1000ths
1 4 . 1 3
7 . 5 0 9

4
MULTIPLYING BY 10, 100 ,1000
0 x 10 x100 x 1000
22.0 220 2200 22000
16.5 165 1650 16500
5
DIVIDING BY 10, 100 ,1000
10 100 1000
19500 1950 195 19.5
234 23.4 2.34 0.234
6
ADDITION AND SUBTRACTION

• LINE UP DECIMAL POINTS EXACTLY
• ADD OR SUBTRACT THE SUM
• E.g. 2.34 18.034 and 234 3.56
• 18.034 234
• 2.34 - 3.56

7
MULTIPLICATION

• 3.45 x 2.1
• Ignore the decimal points
• Multiply as normal
• Put the decimal point back into the answer
• 345
• x21
• Put the decimal point back into the answer. Look
  at the question, there are 3 numbers after the
  decimal place so work the decimal place back into
  the answer.

8
Division

• To divide a whole number into a decimal
• Divide as normal
• Keep the decimal points in line
• Round the answer to sensible number of figures
  where necessary
• E.g. 172.6 4
• Keep the decimal points in line
• 4 Add 0s to the end if
  need be
• Note check by multiplication

9
Divide a decimal by a decimal

• Change the number you are dividing by into a
  whole number.
• Do this by multiplying by 10, 100, 1000
• Do exactly the same to the number you are
  dividing
• Divide to find the answer

10
continued

• E.g. 7.4 0.05
• Multiply the 0.05 by 100 to make it into a whole
• Number. Then do the same to 7.4.
• 5
• Check by multiplication 148 x 0.05 7.4

11
continued

• Find 31.52 2.4
• Multiply 2.4 x 10 24
• Multiply 31.52 x 10 315.2
• 2 4 3 1 5 . 2
• 13.133333333333333333333333
• So we round to 13.13 (to 2 dp)