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Everyday percent problems, solved with numbers you can do in your head — and a calculator to check.
Calculate Sale Price in Your Head: 2-Step Discount
Convert any discount into a "pay this percent" number and compute sale prices before the cashier finishes.
Reverse a Price Raise: 25% Up, What Was It?
From a 25% inflate price back to the original — the divide-by-1.25 trick most people get backwards.
Split a Bill Fairly: 18% Tip Math for Groups
Handle shared tabs, rounded totals and pre-tax confusion without a calculator battle at the table.
Forecast Error: How a 30% Miss Sneaks In
The percentage-error formula behind every optimistic sales and budget projection, with a sanity check.
Turn 85/100 Into a Letter: Grading Math
Score-to-percent conversion and the weighted-average trap that quietly drops your final grade.