The top arithmetic tier: 20 problems, one at a time, with numbers chosen to hurt. Additions pair values from 120 to 600 — "347 + 486" is typical — subtractions start from as high as 800, multiplication reaches 25 × 12, and divisions hide answers up to 50 behind divisors up to 15.
Everything is still calculator-free by design; the ranges are tuned to the edge of what a practiced head can do at pace. There's no time limit and no penalty for wrong guesses — the only opponent is the count-up clock and your previous best.
How to play
One problem at a time, in a fixed sequence — solve the current one to advance.
Type the exact answer and it commits automatically; a wrong answer submitted with Enter shakes, clears, and costs you nothing but time.
The stopwatch starts on your first keystroke and never stops until the 20th problem falls or you give up.
Your finish time is the score — every run is a full clear, so faster is the only better.
What counts in this quiz
20 problems per sprint across all four operations at hard ranges.
Additions use two numbers from 120–600 (sums up to 1,200); subtractions start from 200–800; multiplications run 12–25 times 6–12; divisions are exact with divisors 6–15 and answers 6–50.
Problems are regenerated each run — mastery here means technique, not memorization.
What's not included — and why
Nothing requires pen and paper — the generator deliberately stops short of arbitrary long multiplication, because a mental-math sprint shouldn't secretly be a scratchpad test.
Good to know
The Trachtenberg system of rapid mental calculation was devised by Jakow Trachtenberg while he was imprisoned in a Nazi concentration camp — he built the entire method without paper.
To multiply by 25 at speed, multiply by 100 and divide by 4: 48 × 25 is 4,800 ÷ 4 = 1,200.
Competitive mental calculators describe big additions as "chunking" — processing hundreds, tens, and ones as separate running totals.