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Speed Drill
Pick a mode, set your number, race the clock.
One mistake — restart!
Playing as guest — 5 free tries left, then sign in to keep going.
Stamp
Add the same number 10 times, then subtract back to 0.
e.g. 7 → 14 → 21 … → 70 → 63 … → 0
Best: —
Staircase
Add 1+2+3… up to N, then subtract back down to 0.
e.g. 0 → 1 → 3 → 6 → 10 … → 55 … → 0
Best: —