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MathidiaMathematics Academy
Percentage change and finance
Lesson 11 of 75
Introduction

Percentage multipliers

Objective. Express increases and decreases as decimal multipliers.

  1. 1. Learn
  2. 2. Worked example
  3. 3. Practice
  4. 4. Feedback
  5. 5. Continue

Learn: the key idea

A percentage multiplier is a single decimal that represents a percentage increase or decrease, making repeated or multi-step calculations quicker. To increase an amount by a percentage, add the percentage to 100% and convert to a decimal, so a 15% increase uses the multiplier 1.15. To decrease by a percentage, subtract from 100% first, so a 15% decrease uses the multiplier 0.85. Multiplying the original amount by this single decimal gives the new amount directly in one step, avoiding the need to calculate the percentage separately and then add or subtract it.

Worked example

A price of £40 rises by 20%. Find the new price using a percentage multiplier.

£40.00
Money illustration for £40
  1. 1Write the increase as a percentage of the original: 100% + 20% = 120%
  2. 2Convert to a decimal multiplier: 120% = 1.2
  3. 3Multiply the original price by the multiplier: £40 × 1.2
  4. 4Calculate the result: £48

Answer: £48

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Practice

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Common mistake. Pupils sometimes use 0.15 as the multiplier for a 15% increase instead of 1.15, which only calculates the increase itself rather than the new total amount after the increase.

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