Goal

A number appears on a card, and the card asks one of two questions: odd or even? (gold) or higher or lower than 5? (teal). The left button means odd and lower; the right button means even and higher — so 7 is left for odd/even but right for higher/lower. The question keeps changing; answer as many as you can in 60 seconds.

Levels

• 8 right answers at a level moves you up; 3 misses in a row move you down.
• Level 1 changes the question every 4 cards and shows it a moment early; from level 2 it changes at random; from level 3 it comes with the number.
• From level 5 only the card's colour tells you the question. From level 6 numbers also come as words or dots.
• Levels 7 and 8 give 1.6 and then 1.2 seconds per card.

Scoring

A right answer earns 1 + the level, 1 more if the question has just changed, plus 1 for every 5 in a row (up to +3). A wrong answer costs 3 + the level and half a second. Running out of time costs only your streak.

Switching Questions

Holding two ways of looking at the same thing and moving between them on cue is cognitive flexibility — the skill behind changing plans, juggling tasks and seeing a problem from another side.

Your Switch Cost

You're a little slower right after the question changes. The end card shows how much — and it shrinks as you train.