Thursday, 3 November 2011

Teaching Decimals

In order to introduce decimals to pupils using the following method, they need to have had some previous experience of fractions  (in particular tenths).

1) Draw a rectangle on the board and split it into ten sections. Ask a child how we can label each section of the rectangle (i.e. 1/10). Write 1/10 in each section...




1/101/101/101/101/101/101/101/101/101/10
 
2) Colour some of the rectangles, e.g.


1/101/101/101/101/101/101/101/101/101/10

3) Ask the children what fraction of the rectangle has been coloured (i.e. 1/10 + 1/10 + 1/10 = 3/10).
4) Explain that 3/10 can be written in another way... i.e. 0.3 (no units and three tenths)
5) Explain the features of the notation:
  • The dot in between the 0 and the 3 is called the DECIMAL POINT and we use it to separate the units from the tenths.
  • We always write in the 0 before the decimal point because it reminds us that the whole number is less than one.
  • We say this number as "nought point three" or "zero point three".
6) Now give each pupil a copy of the strips . They should cut out a strip and colour some of the sections (and then stick it in their books). Next, they should write the following information into their books, changing the numbers according to the number of strips that they have coloured.




1/101/101/101/101/101/101/101/101/101/10

7/10 of the strip has been coloured.
7/10 can also be written as 0.7, which we say as "nought point seven" or "zero point seven".
7) Step 6 can be repeated with the pupils colouring different number so sections on new strips.

The trailing zeros after the decimal part of a decimal number

Let’s look at this number 0.650


Decimal point
Tenths/10th
Hundredth/100th
Thousandth/1000th
.
6
5
0


The construction of this decimal part of a decimal number means

6/10 + 5/100 + 0/1000

We can see that 0 out of 1000 is nothing. So we can ignore this 0. What it means is that 0.65 is the same as 0.650

Similarly 0.6500 is the same as 0.65 because it means

6/10 + 5/100 + 0/1000 + 0/10000


Exercises


Questions
Answers
Is 0.34 = 0.340 ?
True
Is 345 = 3450 ?
False
Is 0345 = 345 ?
True
Which one is greater?

.09 and 0.10
0.10
0.0999999 and 0.10000000
0.10000000
3.01 and 2.99
3.01
0345 and 346
346
Is 16 x 10 = 016 ?
False
Is 160.0 = 160 ?
True


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