Correct Math shows you a sum and three possible answers, and gives you only a few seconds to pick the right one before the next question lands.
It stays on addition and subtraction, so the difficulty is not the arithmetic itself but doing it under a clock. Every correct answer adds to your score and the questions keep coming until you miss, which makes this a short, repeatable game rather than something you finish.
One tap or click per question is the entire control scheme. That makes it comfortable on a phone and easy to pick up for a minute between other things, and it is one of the few games here that is genuinely useful as mental arithmetic practice rather than just a way to pass time.
Runs in the browser with no download and no account.