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Row 1                                                              2

Row 2                                                    4        6        8

Row 3                                          10    12        14       16    18

Row 4                                   20   22    24       26      28    30   32

Row 5                          34     36   38     40     42      44    46    48    50

(a) X is 50

(b) By observation,   The first number of row n being 2( (n-1)²+1) 

So for row 20, the first number = 2 ( 19² + 1) = 724

 

(c) The last number of row n = 2n²

 2n² = 1922

n² = 961

n = 31

Row 31 has last number being 1922.

 

Note: Think this question is too difficult for psle. 

 

1 Reply 2 Likes

This is a familiar pattern in chemistry. The max number of electrons in a given shell/energy level (principal quantum number n) is 2n2. However, I think you’re right, they shouldn’t be doing this to PSLE kids.

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