Reverse one digit +-x÷

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.