The bat, the ball, and your brain's first answer
A bat and a ball cost $1.10; the bat costs a dollar more than the ball. If “ten cents” just flashed in your head — congratulations, you're human. That flash is your brain's fast system doing what it does best: answering instantly, confidently, and sometimes wrong.
Psychologists call them System 1 and System 2 — the sprinter and the accountant. The sprinter runs on patterns and gets you through the day; the accountant checks the math but bills by the hour, so the brain avoids waking him unless it must.
Free, about four minutes — see your own result.
Logic puzzles are a gym for exactly one skill: noticing the moment when the sprinter's answer feels right but hasn't been checked. That tiny pause — two seconds of “wait” — is measurable, trainable, and worth more than any amount of trivia.
The ball costs five cents, by the way. If you paused before reading that — the training is already working.