其它
Aline writes a correct calculation. Then she covers two digits which are the same with a sticker:  [insert pic]  What digit is under the stickers? 
Overseas Competition->Knowledge Point->Calculation Modules->Operations with New Definition->Finding Patterns->Encryption and Decryption
Two same digits that add up to "4" in the last digit, hence it must be either 2 or 7.  If we try digit 2, 42+52=94, wrong.  If we try digit 7, 27+57=104. correct. 