Next Percentileby Hetvi Shah Tutoring
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Math · Percentages

SAT percentages: find the right base

The rule

Percent change = (new amount − original amount) ÷ original amount × 100%. Each successive percent acts on the amount at that step.

20% lost80% remains
The original tank is 100%. After losing 20%, 80% remains. The lost part and remaining part both use the original tank as their base.

Worked example

A tank drops from 12,500 to 10,000 liters. What percentage was lost?

  1. The loss is 12,500 − 10,000 = 2,500 liters.
  2. Compare the loss with the original amount: 2,500 ÷ 12,500 = 0.20.
  3. The decrease is 20%. Check: 12,500 × 0.80 = 10,000.

A common trap

Dividing by the final amount gives 25%, which answers a different comparison.

Apply it, then revisit it

Try the skill in a separate question. After checking your answer, explain the step you used and return to any mistake later.

Choose Percentages practice Open the lesson step