Q&A - PSLE Math

[ChiefKiasu]

lantian:

http://farm4.static.flickr.com/3010/2898264072_99252aab49_o.jpg\">

Sigh... I'm still trying to learn to think like you

[corneyAmber]

Sorry to differ a little here with lantian. A small error but big in concept.


Technically speaking(since this is math and precision is impt hence its concept), it is not correct to name the first 2 boxes as A and B in each of the peach box. Can only put the 2 boxes together as
(A+B) to be reflecting the question more accurately. The concept is to know that (A+B) = 2 units of its average and not A=B=1 unit each.

Example:
A=3, B=5, then A+B = 3 + 5 = 8. Avg = 8/2 = 4.
this implies A+B = 2*4 = 8 but does not imply that A=4 and B=4.

Even though the answer is correct, the concept of A=B=1 unit is a wrong assumption to get to the answer.

It might just be an oversight when lantian drew the diagram but thought I should point it out that potentially the working cud be marked wrong for concept.

[ChiefKiasu]

ks2me:

...Technically speaking(since this is math and precision is impt hence its concept), it is not correct to name the first 2 boxes as A and B in each of the peach box. Can only put the 2 boxes together as

(A+B) to be reflecting the question more accurately. The concept is to know that (A+B) = 2 units of its average and not A=B=1 unit each...

Yes, the labelling is not correct, but lantian did color all the similar boxes with the same color, so I guess that's his intention, anyway. Thanks for clarifying!

[lantian]

[quote]
Sigh... I'm still trying to learn to think like you :)[/quote]Hi Chiefkiasu

The underlying principle is to see Maths through the eyes of our children. Try our best to solve problems using Problem solving strategies within the syllabus. Sit down with our kids when they encounter problems and you’ll be surprised by how fertile their young minds are when coming up with simple solutions to difficult problems. Enjoy the journey.

[lantian]

There are three conditions which will give the same average number. First case, A is greater than B. Second case, B is greater than A. In the last case, A is equal to B. It’s not illogical to assume that A has the same value as B. After going through with my son, we chose to use the last scenario to show as the model for our solution.


You may choose to represent your solution in a different way

http://farm4.static.flickr.com/3265/2901723766_130f7070f2_o.jpg\">

[heutistmeintag]

My son came back today with this PSLE question btw I am not sure if he had recalled the full question.


Brian invited some boys and girls, there are 20 more boys than girls. 3/4 of the boys and 2/3 of the girls managed to come, how many children did Brian invite?

I cant figure this out because there seems to be too little info to work with. For example the 2nd statement doesnt provide a mathematical relationship.

[kiasuson]

According to my son, another information given is that there are 19 children that did not turn up.

[kiasuson]

My son’s answer is 68 and I think he is correct.

[heutistmeintag]

oh i see, now I can solve by alegbra.


B=20+G

1/3G+1/4B=19
4G+3B=19*12=228
4G+3*(20+G)=228
4G+60+3G=228
7G=228-60
7G=168
G=24
B=20+24=44
Total number of children invited is (24+44)=68

ok, can someone explain using modelling?

[heutistmeintag]

kiasuson:

My son's answer is 68 and I think he is correct.

Thanks for providing the missing link. Happy for your son but sad for mine, he didnt get it.