~/math

Math

Trading firms and some quant-leaning teams screen software engineers with mental arithmetic and probability. Both get faster with practice.

Mental math

Arithmetic against the clock. Keyboard only: type the answer, Enter, next.

2-minute sprint 5 minutes 8-minute test

Probability puzzles

Next puzzle

Expected value, conditional probability, Bayes and counting. Exact answers (type 7/36 or 0.5). Solved ones come back for review.

Expected value

Waiting for a six easy · new Two dice, the bigger one easy · new Seeing every face medium · new Two heads in a row medium · new Heads then tails medium · new Roll or stop medium · new

Linearity of expectation

Hats back to their owners easy · new Counting runs medium · new How many faces show up medium · new Cards before the first ace hard · new Shared birthdays easy · new New records hard · new

Conditional probability

At least one girl medium · new A six is showing easy · new Three doors medium · new Two cards, both red easy · new Taking turns with a die medium · new Same color medium · new

Bayes

A positive test medium · new Which coin? medium · new Which urn? easy · new Testing twice hard · new Spam words medium · new Loaded die medium · new

Counting

Full house medium · new A committee easy · new Grid paths easy · new Nobody gets their own medium · new Three dice summing to 10 medium · new Birthday problem medium · new

Classics

Gambler's ruin medium · new Breaking a stick hard · new Back to the start medium · new Adding uniforms hard · new Three rolls, best stop hard · new More heads medium · new
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