Transcript DECIMALS - Home Page | Skills Workshop

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?
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DECIMALS
DECIMALS
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PLACE VALUE
Hundreds
100s
Tens
10s
Units
1s
.
Tenths
10ths
Hundredths
100ths
1
4
.
1
3
7
.
5
0
Thousandths
1000ths
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MULTIPLYING BY 10, 100 ,1000
0
x 10
x100
x 1000
22.0
220
2200
22000
16.5
165
1650
16500
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DIVIDING BY 10, 100 ,1000
÷ 10
÷ 100
÷ 1000
19500
1950
195
19.5
234
23.4
2.34
0.234
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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
+2.34
234
- 3.56
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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.
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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
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Add 0s to the end if need be
Note – check by multiplication
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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
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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.
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Check by multiplication – 148 x 0.05 = 7.4
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continued
• Find 31.52 ÷2.4
Multiply 2.4 x 10 = 24
Multiply 31.52 x 10 = 315.2
24 315.2
= 13.133333333333333333333333
So we round to 13.13 (to 2 dp)
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