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Three everyday percentage problems, solved as you type.
X% of Y = (X/100)×Y. X is what % of Y = (X/Y)×100. Percent change = ((new−old)/|old|)×100 — positive means increase, negative means decrease. Worked example: 20% of 150 = (20/100)×150 = 30. A price rising from $50 to $65 is ((65−50)/50)×100 = 30% increase.
Multiply the price by 0.80. A $250 item at 20% off costs $200 — the same as "what is 80% of 250" above.
Going from 20% to 25% is a 5 percentage point rise but a 25 percent increase (5/20). News headlines mix these up constantly.
Multiply by (1 + p/100). Adding 8% tax to $50: 50 × 1.08 = $54.