Reverse one digit +-x÷ [for iOS]

This App "Reverse one digit +-x÷" is a arithmetic training App. And this is a searching game, too. This App is a Reverse version of my App "one digit +-x÷";

This App has four categories, addition:"Reverse one digit +" subtraction:"Reverse one digit -" multiplication:"Reverse one digit x" and division:"Reverse one digit ÷". Each category has 9 questions on nine stages, random 81 questions.

ex.
"one digit +" : Find '4 + 8' from '12'.
"one digit -" : Find '10 – 6' from '4'.
"one digit x" : Find '9 x 9' from '81'.
"one digit ÷" : Find "12 ÷ 3" from '4'.