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Question

My DD briefly told me she couldn’t complete this question in PSLE. She was using algebra (again) and trying to figure out “the formula”. I didn’t have time to dwell on this until Science paper today. Someone sent me one online solution for this questions yesterday and I took a look and trust in my heart that MOE will not set such “killer” question so I try to stand outside the box, and find a simpler way. And I found it below, I think.

(Part A is FOC marks, to encourage kids to do attempt to complete this table to see the pattern for Part B) Though I’m not sure if the table has a row for “Total no. of triangles”, which is very important here.

(Part B is to deduce formula of perfect square)  250 x 250 = 62,500#

(Part C solution: If we cancel out the white and grey, the remainder is the figure nth number (odd white or even grey) So in 250th figure, there are extra 250 grey triangles.

So no. of white triangles = (62500-250)/2 = 31,125

So % of grey triangles = (31,125 + 250)/62500 = 50.2%#

I think what could be the simple way of thinking of the setter may not be so simple for kids of P6, especially those of MO, GEP, formula-taught kids. And understandably, this is a misalignment that cause some parents or students to be upset. Hope we all can see the beauty of simplicity and enjoy Maths or enjoy teaching Maths in a simpler way.

Answer

a)
Method 1 :
1 + 5 + 9 = 15 (white triangles)
3 + 7 = 10 (grey triangles)

Method 2 :
5 x 5 = 25
25 – 5 = 20
20/2 = 10 (grey triangles)
10 + 5 = 15 (white triangles)

b)
250 x 250 = 62500 (grey and white triangles)

c)
250 x 250 = 62500
62500 – 250 = 62250
62250/2 = 31125 (white triangles)
31125 + 250 = 31375 (grey triangles)
(31375/62500) x100% = 50.2%

Ans : a) 15 (white), 10 (grey); b) 62500 (grey and white) and c) 50.2%

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