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My answer is 272727.
This is how I worked it out. If you take the first example and set
it out like this: (9+) 12 = 21 I worked out that 21 - 12 = 9 and
the same with 51 - 15 = 36 (second example).
Therefore 414141 - 141414 has to equal the secret number, which is
272727.
Solution 2
From Hang Hao who goes to Pei Hwa
Presbyterian Primary School, Singapore:
The answer to this problem is 272727.
Reversing 141414 gives 414141.
The secret number add 141414 gives 414141.
Therefore the secret number is obtained by 414141-141414 =
272727.