Crazy Arithmetic

This is a masochistic arithmetic game, your score will be shown on google play game leaderboard.
Game sounds simple, but challenging, looks like a simple one-digit addition and subtraction question, in fact, it's very difficult.
For example, the first question is 1 +1 =?, But will not let you answer it immediately, until the second question shown and the first question to be hidden away, when you can answer the first question.
Well, maybe you think it is simple, the first few questions indeed the case, but the next question is indeed difficult.
With increasing difficulty, the latter may be the subject let you see 1-4 questions, and then let you answer the first question, then you also need to remember the fifth question, it is very challenging.
This game integrated google play achievement system and leaderboard, come to challenge the game, let your friends are surprised your scores.