Reverse one digit arithmetic

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'.Fun Reverse thinking.