Percentage problems

Percentage problems come in three kinds: find the part, find the percentage, or find the whole.

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Part: percentage × whole ÷ 100.
Percentage: part ÷ whole × 100.
Whole: part ÷ percentage × 100. Discounts: find the percentage, subtract. GST: add 10%.

80% of a number is 120. What is the number?

If 80% is 120, then 1% is 120 ÷ 80 = 1.5, and 100% is 1.5 × 100 = 150.

Answer: 150

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Divide by the whole, not by the part.

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