Math calculators here cover the operations people actually reach for outside a classroom: percentage changes, averages and spread, probability and combinatorics, equation solving and unit conversion. They suit students checking homework, analysts sanity-checking a figure, and anyone who wants the arithmetic done without the risk of a slipped decimal.
13 calculators in this category
Percentage questions come in three shapes and mixing them up is the most common source of error. 'What is 15% of 240' scales a number. 'What percent is 36 of 240' finds a ratio. 'What is the change from 240 to 276' measures growth relative to a starting value. The third is direction-sensitive: a rise from 200 to 250 is a 25% increase, but the fall from 250 back to 200 is a 20% decrease, because the base changed.
The same asymmetry explains why a 20% discount followed by a 20% price rise does not return the original price — successive percentages multiply rather than add.
The mean is the total divided by the count and is pulled hard by outliers; the median, the middle value once sorted, is not. When a data set is skewed — incomes, house prices, response times — the median usually describes a typical case better.
Spread matters as much as centre. Standard deviation measures the typical distance of values from the mean, and it distinguishes a set clustered tightly around 50 from one bouncing between 10 and 90 with the same average. Note the difference between the population formula, which divides by n, and the sample formula, which divides by n − 1 to correct for the bias that comes from estimating the mean from the sample itself.
Probability problems usually reduce to counting outcomes. Permutations count arrangements where order matters, combinations count selections where it does not, which is why lottery odds use combinations. For equations, the quadratic formula solves any expression of the form ax² + bx + c = 0, and the discriminant b² − 4ac tells you before you finish whether you will get two real roots, one repeated root, or a complex pair.
Use the sample version, dividing by n − 1, when your numbers are a subset drawn from a larger group and you want to estimate that group's spread. Use the population version only when your data covers every member of the group you care about.
Each percentage is applied to a different base. A 30% drop from 500 gives 350, and a 30% rise on 350 only gives 455. To reverse a percentage change you divide by the multiplier rather than applying the same percentage in the opposite direction.
Each math calculator page includes a worked example that runs the formula through realistic numbers step by step, so you can follow the same route by hand and check where your own answer diverged.
Calculations run in standard double-precision floating point and results are rounded for display. That is exact for everyday arithmetic; if you are chaining many operations, work from the unrounded intermediate values rather than re-entering rounded ones.