usaik:

Hi Modelmatics,

Your explanation is extremely clear and hit on the nails those things which I couldn't explan to my kid. :thankyou:

Hi usaik,

You're most welcome. Glad to be of help.

Hi usaik,


To estimate means that we do not need to perform any calculation/working. You can explain to your kid that when we estimate, we want a rough answer quickly, thus we do some quick and convenient mental calculation.

When we perform addition or subtraction estimation, we usually approximate to the nearest tens, hundreds, thousands, etc. However, when we perform multiplication and division estimation, we make use of convenient numbers, i.e., the multiples of numbers/multiplication tables.

For primary kids, they are only required to learn up to 10 times tables. Hence, when they estimate, they should use 2 digits multiples which can be found in the 1 to 10 times table (i.e., 1 x 1 all the way to 10 x 10).

For this question, the first 2 digits are "37" (from the number "372"), thus we use the multiple of "4" closest to "37" which is 36. Therefore, we round it up to "360" making very easy to perform a quick mental calculation, i.e., 36 ÷ 4 = 9, thus 360 ÷ 4 = 90.

For PSLE, the kid’s answer should look like this:

372 ÷ 4 =(here should use "approximately equal to" sign) 360 ÷ 4 = 90

Smosh:

Hi guys!


Anne has $165 and Cally had $200 at first.
After spending an equal amount of money, Cally had twice as much money as Anne. How much money did each of them spend?

I was able to solve it by algebra, but my son in P4 cant use it.
Anyone able to help me with the correct method of solving?

Thanks so much in advance

This question involves the <a href=\"http://www.teach-kids-math-by-model-method.com/constant-difference-concept.html%22%3EConstant Difference Concept</a> as well as the Working Backwards Heuristics.

Step 1: It is easier to work backwards by drawing the \"After\" model first. Since Cally had twice as much money as Anne in the end, we draw 2 boxes to represent Cally's money and 1 box to represent Anne's money. We leave a big gap on the left of the model to add in the \"Spent\" part later. (This aids visualisation)

http://postimage.org/image/m6rlodj8/

Step 2: Since both of them spent an equal amount of money, we draw 1 box each (of equal size) to the left of both of their models to represent the same amount of money spent.

http://postimage.org/image/m8qpsaro/

Step 3: As Anne has $165 and Cally had $200 at first, we put these 2 values into the model.

http://postimage.org/image/m93y32pw/

From the model,

1 unit ----------> $200 - $165 = $35

From Anne's model,

Amount spent = $165 - $35 = $130

Therefore, they spent $130 each.

Smosh:

Hi!


Anne has $165 and Cally had $200 at first.
After spending an equal amount of money, Cally had twice as much money as Anne. How much money did each of them spend?

I was able to solve it by algebra, but my son in P4 cant use it.
Anyone able to help me with the correct method of solving?

Thanks so much in advance

Hi Smosh,

You can also teach your kid using the Model Method.

Step 1: This question involves the <a href=\"http://www.teach-kids-math-by-model-method.com/constant-difference-concept.html%22%3EConstant Difference Concept</a>, i.e., the difference between the 2 variables remains a constant before and after the transfer (the spending of an equal amount of money). It would be easier to work backwards starting with the \"After\" model and work back to the \"Before\" model. We first draw 2 boxes to represent the amount of money Cally had and 1 box to represent the amount of money that Anne had.

http://postimage.org/image/1xq3kz9z8/

Step 2: Next, we draw a box each to the left of both Cally's and Anne's model to show the equal amount of money both had spent.

http://postimage.org/image/1xr3yswuc/

Step 3: Then we label the amount of money that Anne had before the spending as $165 and the amount of money that Cally had before the spending as $200.

http://postimage.org/image/1i6qeln38/

Step 4: From the model, we can see that the difference between Anne and Cally's money is equivalent to 1 unknown unit (represented by \"?\").

http://postimage.org/image/1i6tpoc2s/

Thus,

1 unit ----------> $200 - $165 = $35

Putting the value of 1 unit = $35 back into Anne's model,

$165 - $35 = $130

Therefore, both of them spent $130.