NumNumPanic ~ Trick Formula ~

It looks super simple formula. However, the calculation rules will change depending on the color.
You are not misled by the gap of look and answer, or will continue to select the correct answer?
Judgment is called into question, brain training game!

[Rules]
To calculate a formula that is displayed on the screen, please press the button that correct answer was written.
However, by the color of the formula, the calculation method will change.
Black: The calculated to display street
Red: Always addition
Blue: Always subtraction

Score will increase 1 When you correct answer.
Time limit when you wrong answer will reduce 10 seconds.
Time limit in the initial state is 30 seconds.
Time limit will increase 5 seconds each time you answer 10 questions.

[Play mode]
Normal: The choices are two. Left as a result of the addition is, right appears subtraction results.
Hard: The choices are four. Answer that appear in the choices are swapped randomly.