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Reverse Trick

Stage: 2 Challenge Level: Challenge Level:1

Solution 1
From Jonathan at St. Andrew's Primary School, Cullompton:

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.