1. © 2009 Mathematics Department Hougang Primary School

2. © 2009 Mathematics Department Hougang Primary School Approximate Sign vs Equal Sign When do we use ‘≈’ or ‘= ’ in our number statements ?

3. © 2009 Mathematics Department Hougang 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.

4. © 2009 Mathematics Department Hougang 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.

5. © 2009 Mathematics Department Hougang Primary School Using unitary method to solve word problems E.g. 40% —— $1 600 10% —— 1 600 ÷ 4 = $400 100% —— 10 x 400 = $4 000 40% = $1600 100% = $4 000   This is because amount of money is not the same as %.

6. © 2009 Mathematics Department Hougang 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.

7. © 2009 Mathematics Department Hougang 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

8. © 2009 Mathematics Department Hougang 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 

9. © 2009 Mathematics Department Hougang Primary School Conversion of unit of measurements during intermediate steps E.g. 52 litres = 52 000 cm 3 52 litres = 52 000 52 litres —— 52 000 Units missing 

10. © 2009 Mathematics Department Hougang Primary School John gave of his stamps to Peter. If he gave 16 stamps to Peter, how many stamps did he have at first? = 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.

11. © 2009 Mathematics Department Hougang Primary School —— 16 BUT 1 —— 8 x 16 = 128 Or we can also use the unitary method : 1 unit —— 16 8 units —— 8 x 16 = 128 John had 128 stamps at first. Here the fraction represents a whole number.

12. © 2009 Mathematics Department Hougang Primary School Percentage Write as a percentage. Many pupils will do this: =  Why? This is incorrect because -%-% is missing! - is not the same as itself x 100 ! = 75%

13. © 2009 Mathematics Department Hougang Primary School Write as a percentage. SO = = 75% Or we can also use the unitary method : 4 units —— 100% 3 unit —— = 75%