Percent Change, Discounts and Interest
Percent change divides by the old value. Use multipliers (1 + r) and (1 − r) to find new values, undo them by dividing, and chain them for successive changes. Discounts, mark-ups and simple interest use the same idea.
What it is
This lesson uses the percent template from L13 in situations where an amount changes: prices go up or down, salaries are raised, items are marked down, money earns interest.
The key idea is the multiplier. A 15% increase means the new amount is 115% of the old one, so you multiply by 1.15. A 15% decrease leaves 85%, so you multiply by 0.85.
Why it matters on the exam
Percent change, discounts and interest are standard word problems in Numerical Ability. They are also where the exam sets its best-known traps: dividing by the new value, adding the percent back to a sale price, and adding two percents in a row.
In daily work you use them to compare budgets, read price increases, check a store's discount, or compute a loan's interest.
- ₱7,884.80
- ₱8,000
- ₱8,948
- ₱10,035.20
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- How to recognize it on the test
- What to look for (6 checks)
- All 8 rules and tools
- 3 worked examples, every step explained
- 7 common mistakes and how to fix them
- 3 exam techniques
- Remember: 6 key points
- Practice questions with explanations, and your progress saved
More Numerical Ability lessons
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