© 2009 Mathematics DepartmentHougang Primary School

© 2009 Mathematics DepartmentHougang Primary School

Approximate Sign vs Equal Sign

When do we use ‘≈’ or ‘=’ in our number statements?

© 2009 Mathematics DepartmentHougang Primary School

1 678 = 1 680

Which is correct?

or

1 678 ≈ 1 680

1 678 is not the same as 1 680.

1 680 is an approximate value of 1 678. Therefore ‘≈’ must be used.

© 2009 Mathematics DepartmentHougang Primary School

Which is correct?

6 345 m = 6 345 m

6 345 m ≈ 6 345 m

or

6 345 m is not an approximate value of 6 345 m.

6 345 m is an exact value of 6 345 m. Therefore ‘=‘ must be used.

© 2009 Mathematics DepartmentHougang Primary School

Using unitary method to solve word problemsE.g.

40% —— $1 60010% —— 1 600 ÷ 4 = $400100% —— 10 x 400 = $4 000

40% = $1600100% = $4 000

This is because amount of money is not the same as %.

© 2009 Mathematics DepartmentHougang Primary School

Ali and Shawn have a total of 210 stamps.Shawn has twice as many stamps as Alan. How many stamps does Shawn have?

3 units —— 210 1 unit —— 210 ÷ 3 = 70 2 units —— 2 x 70 = 140

Shawn has 140 stamps.

© 2009 Mathematics DepartmentHougang Primary School

Dollar and cent notation

Muthu bought a pen for 40 ¢ and a book for $1.40.

How much did he spend altogether?

Amount spent altogether

= $1.40 + 40 ¢

= $1.40

© 2009 Mathematics DepartmentHougang Primary School

Dollar and cent notation Muthu bought a pen for 40 ¢ and a book for $1.40.How much did she spend altogether?

Amount spent altogether= 1.40 + 40= $1.80

© 2009 Mathematics DepartmentHougang Primary School

Conversion of unit of measurements duringintermediate steps E.g.

52 litres = 52 000 cm3

52 litres = 52 000

52 litres —— 52 000 Units missing

© 2009 Mathematics DepartmentHougang Primary School

8

1John gave of his stamps to Peter.

If he gave 16 stamps to Peter, how many stamps did he have at first?

8

1= 16

1 = 8 x 16 = 128

A fraction is not equal or the same as a whole number!

Note :

The answer may be correct but the method is wrong and therefore no mark will be awarded.

© 2009 Mathematics DepartmentHougang Primary School

8

1—— 16

BUT

1 —— 8 x 16 = 128

Or we can also use the unitary method :

1 unit —— 168 units —— 8 x 16 = 128

John had 128 stamps at first.

Here the fraction represents a whole number.

© 2009 Mathematics DepartmentHougang Primary School

Percentage

Write as a percentage.4

3

4

3

Many pupils will do this:

= 1004

3x Why?

This is incorrect because-% is missing!

- is not the same as itself x 100 !4

3

= 75%

© 2009 Mathematics DepartmentHougang Primary School

Write as a percentage.4

3SO

4

3= %x100

4

3 = 75%

Or we can also use the unitary method :

4 units —— 100%

3 unit ——

= 75%

4

1003