The three questions people actually ask
Almost every percentage problem is one of three shapes: finding a part from a percentage ("what is 15% of 80"), finding a percentage from two numbers ("12 is what percent of 80"), or finding the whole from a part and a percentage ("12 is 15% of what").
They are the same equation rearranged: part = percent ÷ 100 × whole. Identify which term is missing and the arithmetic follows.
Percentage points are not percentages
If an interest rate rises from 4% to 5%, that is a one percentage point increase but a 25% increase in the rate itself. News reports blur these constantly, and the difference is enormous when the base is small.
Similarly, a 50% fall followed by a 50% rise does not return you to the start — it leaves you 25% down, because the rise is calculated on the smaller number.
Frequently asked questions
Why is 15% of 80 the same as 80% of 15? +
Both compute 0.15 × 80 = 12. Multiplication is commutative, which makes some mental arithmetic much easier — 4% of 75 is awkward, but 75% of 4 is obviously 3.