Math & Education

How to round numbers: if the next digit is 5 or more round up, otherwise round down. Covers decimal places, significant figures, and the exactly-5 case.

How to calculate percentage increase and decrease: multiply by (1 + decimal) or (1 – decimal). Worked examples, plus the increase-then-decrease trap.

How to calculate perimeter: add up all the sides. Formulas for rectangles, squares, triangles, and circles, with examples and perimeter vs area.

How to calculate a ratio: write it with a colon and simplify by dividing by the greatest common factor. Learn to scale ratios and convert to percentages.

How to calculate the average: the mean, median, and mode explained with one worked example, plus when to use each type of average.

How to convert a fraction to a percentage: divide the top by the bottom and multiply by 100. Includes examples, a conversion chart, and the reverse.

Percentage change vs percentage difference: change divides by the original value, difference by the average. See both formulas worked on the same numbers.

Master the three percentage formulas – percentage of a number, X as a percent of Y, and percentage change – with worked examples and mental-math shortcuts.