Brainlag Plus
Brainlag PlusRepeated proportional change
Use a multiplier for each percentage change, work year by year with and without a calculator, compare savings accounts and growing or shrinking populations, and (Higher) go backwards or take money out each year.
One multiplier for each change
A percentage change is a multiplication. A rise of 4% multiplies by 1.04; a fall of 4% multiplies by 0.96. Repeat it n times and you multiply by the multiplier to the power n.
- £5000 at 3% compound interest for 4 years
- multiplier = 1.03
- 5000 × 1.03⁴ = 5627.544...
- £5627.54
Changes do not add. A rise of 10% then a fall of 10% gives 1.1 × 0.9 = 0.99, a 1% fall overall, not 0%.
The rest of this lesson and its 10 practice questions are in Plus.
Screen 1 of 4, free to read.
- 10 exam-style questions, marked as you go, each with a worked solution
- The Scientific Calculator beside every question
- Anything you get wrong is saved to your flashcards