entei17\" post_id=\"1939792\" time=\"1570178140\" user_id=\"162440:I think your solution is still overly complicated. There is no need to shift the semi-circles nor visualize anything. The solution is just 3 lines, does not involve algebra and easier than model method:Totally agree, the solutions presented so far are too complex. Don't use algebra or units & parts to confuse the kid. In fact, this qn does not involve any properties of circle either. You just need to see that the overlapping parts are of the same length then you can use logic to derive the other parts. Pls see my pic and logic here.jumpingjacks\" post_id=\"1939677\" time=\"1570118362\" user_id=\"56373:[quote=Iluvmygals post_id=1939672 time=1570115299 user_id=26453]I think the solutions by the tuition centers over complicate the questions.
Just need to focus on the 2 semi circles by the side you will see the length. Don't need algebra, don't need shift the semi circles here and there.....simple circle properties will do.
https://postimg.cc/bZpQGXVK
1. The green line shows the part where the 2 semicircles overlap: they are of the same length on each of the semicircle.
2. Hence, the orange lines must be the same length (i.e. 22cm) as the semicircles are identical.
3. Thus, you can derive the purple part as 22-12=10
Do the same for the other side (highlighted in pink) then you can add them to get 10 +16+10=36
Hence the working can be done in just 2 or 3 lines.
https://postimg.cc/TKbsrNmV
Top=Bottom
3D + 12 + 12 = 2D +22 + 22 +16
D = 36
As for the triangle question part (c), the suggested solution by one of the tutor is overly complicated too, and he is a tutor! Primary school maths and national exams do not need rocket science to solve, to a certain extent,it extends to math olympiad questions too. So one additional heuristic should be added to the top of your tools, and that's the maxim \"PSLE question is meant to be easy, there has to be a shortcut somewhere.\"
The solution for the triangle question part (c) is:
Note that the difference between the white and grey triangles are 1, -2, 3, -4, 5, -6,....., 249, -250
So there are 250 more grey triangles than white triangles
So there are (62500-250) / 2 = 31125 white triangles
31125+250=31375 grey triangles
But even though the questions do not need elaborate solutions, it does not mean they are easy to comprehend and frame a solution, especially when most PSLE students would not have exposure to these question styles. This put an unfair advantage to GEP, E2K students and MO trained students who have gotten exposure to these question types. There is also an element of luck in being able to find the key to the above solution. Under exam stress and time constraint, sometimes you just can't 'see' it.
MOE promulgate the belief that all schools are good schools. I agree, but I also believe that some schools are better. The better schools would be able to better prepare/expose the students for these questions. The field is not even, and toughening the PSLE would make the field even more uneven. This totally run contrary to MOE's new mission to de-stress the educational system. The trend of tougher questions simply pushes parents to seek more help to tackle them, math olympiad classes will get more business and less well off students get left behind. OYK was still asking parents not to send their kids to tuition centres when they scrap some of the exams? The change to the AL system is supposedly for students to be graded based on their individual performance and they will no longer be as finely differentiated. If you are setting a tough question that almost every student has not seen before, then fine. But if some have better exposure, then they are definitely well differentiated.[/quote]Actually i think i understand the previous person's one better than urs...
