The most frequent percentage errors: using the wrong base, calling a doubling a 200% increase, adding successive discounts, mixing up points and percents, and averaging percentages that have different totals.
Profit percentage and markup use cost as the base; margin uses selling price. See the three formulas, a shared example with a cost of 80 and a selling price of 100, and when each figure is the right one.
Convert any fraction to a decimal or a percentage, and go back again, including repeating values such as 1/3 and 2/3. Includes worked examples and a short method for each direction.
Successive percentage changes multiply; they do not add. See why a 10% rise followed by a 10% rise is 21%, and why +20% then −20% leaves you 4% down.
Percentage error is the absolute difference between an experimental value and an accepted value, divided by the accepted value, times 100. See the formula, examples, and how it differs from percentage difference.
Convert exam marks to a percentage with the standard formula, combine more than one paper correctly, and see why CGPA-to-percentage rules depend on the institution.
Two discounts of 20% and 10% are not 30% off. Learn how successive percentage discounts compound, with worked examples and a simple way to find the combined percentage off.
Learn how to work backwards from a percentage to the original number, including sale prices and values after an increase, and why a 100% reduction cannot be reversed.
A move from 4% to 6% is 2 percentage points, but a 50% increase. Learn the difference between a percentage increase and percentage points, with clear examples.
Learn how to calculate a percentage from a part and a whole, take a percentage of a number, and convert a decimal to a percent, with step-by-step examples.
