Articles

Learn how to calculate a percentage the easy way. Find X% of a number, work out what percent one number is of another, and use fast mental math tricks.

A five-number summary lists the minimum, Q1, median, Q3, and maximum. Learn to read spread, skew, and outliers from a box plot, with a worked example.

Percentiles and quartiles explained simply: a percentile is the percent of data at or below a value, and quartiles split sorted data into four equal parts.

A z-score tells you how many standard deviations a value is from the mean. Learn the formula z = (x – mean) / SD, a worked example, and the empirical rule.

Learn to calculate sample size with the formula n = z^2 * p * (1 – p) / e^2. A worked example gives n = 385 at 95% confidence and a 5% margin of error.

Standard deviation measures how spread out data is around the mean. See the formula in plain English, a full worked example, and population vs sample simply.

Learn how to find the median of a data set in three simple steps: sort the numbers, find the middle value, and average the two middle numbers if the count is even.

Mean, median, and mode explained simply: the mean is the average, the median is the middle value, and the mode is the most frequent value. See when to use each.

GPA scales around the world differ by country: US 4.0, India 10-point, UK honours, Germany 1 to 5, and ECTS A-F. See how they compare and why conversion stays approximate.

Attendance percentage is classes attended divided by total classes, times 100. See the formula, a worked example, and how many classes you can safely miss.