Using Comparison Concept
In Singapore, most kids at lower primary should have enounter math problems using comparison of numbers. For example is 3 more than 20 is ________.
6 less than 20 is ________. Many of the kids find the question abstract so rely on cue words like "more than is always addition" and "less mostly is subtraction".
The problem rely on the cue words may seem to work most of the case, but if it is not robust and even it work all the time, your kid will suffer in understanding the
underlying math logic behind the question. It is always important to train your kid to understand rather than apply the rule (just follow and don't ask why).
For example to solve below simple equation
8 more than 20 is _______.
| more than
------------> |
| 20 |
8 |
|
| ? |
Using the model method, we can translate the math statyement into a more concrete representation.
In Singapore school system, we usually used a bar diagramas shown above. For above example, the question
8 more than 20 means the the value must be more than 20 as the value of 8 is added into it.
Notice that 20 is the first number after the words 'more than'. Draw a bar that represent the starting number 20. Then draw a
shorter bar represent the added on value (value of 8). Also use an arrow above the bar to indicate the 'add on' status.
Explain to your child on the graph representation. Telling him/her that to get the result, he/she need to get the two values from both bars to be summed.
Hence the answer is 20 + 8 = 28.
Now we look at another question : 7 less than 15 is __________.
As the word "less than", the meaning is "subtracted from" so the meaning of the question is "7 subtracted from 15".
Now we need to reverse from the previous question. The first number is 15 which is the whole. Next will be the subtracted value which is 7.
| 15 |
| less than
<-------- |
| ? |
7 |
Finally is the unknown bar. The unknown bar and the bar represent the value 7 sum up together to give the total value of 15.
To get the value of the unknown bar, you need to subtract 7 from the whole value of 15.
The working is : ______ = 15 -7 = 8
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