Quant Mental Math Fractions Guide
Quant mental math fractions guide for probability, expected value, odds, complements, simplification, and interview drill design.
Candidates slowed down by fractions in probability and expected value problems.
Fractions appear everywhere
Probability answers, odds, expected values, dice ratios, and card counts often start as fractions. Fraction fluency keeps the reasoning visible instead of burying the answer in decimal noise.
Memorize benchmarks
Know common conversions such as 1/8 = 12.5 percent, 1/6 about 16.7 percent, and 1/3 about 33.3 percent. Benchmarks make estimates faster and easier to check.
Concrete example
If a probability is 5/36, compare it with 1/6 = 6/36. The answer is slightly less than 16.7 percent, so a decimal around 13.9 percent is plausible.
Simplify before multiplying
Cancel common factors before multiplying large numerators and denominators. This reduces arithmetic errors in combinatorics and expected value calculations.
Common mistakes
Candidates often convert every fraction to a decimal too early. Keep exact fractions while reasoning, then convert only when the format requires it.
Practice the pattern
Use the LeetQuidity curriculum and calibration to turn this topic into a focused practice plan.