Mathematics
Statistics, fractions, primes, equations and plane geometry, worked out exactly and drawn to scale.
Each of these applies a stated rule and shows the working, because the interesting part of a wrong answer is usually which convention was used. Where two conventions are both defensible — a sample standard deviation against a population one, or which of several ways to place a quartile — the page says which one it applied.
Area and perimeter of nine plane shapes, each one drawn to scale with the measurements you gave.
Combinations and PermutationsCount the ways to choose r things from n — with or without order, with or without repeats.
Cubic Equation SolverSolve ax³ + bx² + cx + d = 0 — all three roots, complex ones included, and whole ones written as whole numbers.
Fraction CalculatorAdd, subtract, multiply and divide fractions exactly, reduced and as a mixed number.
GCD and LCM CalculatorThe greatest common divisor and least common multiple of two numbers or of a whole list.
Mean, Median, Mode and Standard DeviationDescribe a list of numbers, with both the sample and the population standard deviation.
Prime FactorisationBreak a whole number into its prime factors, list its divisors and check whether it is prime.
Quadratic Equation SolverSolve ax² + bx + c = 0 with the discriminant, the vertex and the roots — complex ones included.
Rule of ThreeFind the fourth number of a proportion — direct or inverse, because the two give different answers.
Triangle SolverFind every side, angle and the area from three measurements — and both triangles when there are two.
Volume and Surface Area CalculatorVolume and surface area of ten solids, each one drawn and each formula shown with your numbers in it.
Weighted Average CalculatorAverage grades with their weights, and find the grade the next test needs for the average you are aiming at.