Percentage problems appear on every single SAT. They seem simple, but the College Board designs them to exploit common errors. Here are the 5 traps to avoid.
Mistake 1: Adding Successive Percentages
The trap: A price increases by 20%, then decreases by 20%. Students assume the price returns to the original.
Reality: It does NOT.
Start with 100$:
- After 20% increase: 100 \times 1.20 =
- After 20% decrease: 120 \times 0.80 =
You lost 4! The correct approach is to multiply the multipliers: (a 4% net decrease).
Mistake 2: Using the Wrong Base
The trap: A shirt was 80. Students calculate: increase.
Reality: Percent change uses the original value as the base, not the new value.
Always divide by the starting number.
Mistake 3: Confusing "Percent OF" vs "Percent MORE"
The trap: "A is 30% more than B" is NOT the same as "A is 30% of B."
- 30% of 200
- 30% more than 200
On the SAT, read the wording very carefully.
Mistake 4: Forgetting to Reverse a Percentage
The trap: After a 25% discount, a laptop costs 600$. What was the original price?
Wrong: 750$ ✗
Right: is 75% of the original. , so 800$ ✓
Mistake 5: Compound vs Simple Interest
Simple interest: (interest on principal only)
Compound interest: (interest on interest)
After 3 years at 10% on 1000$:
- Simple: 1300$
- Compound: 1331$
The SAT will specify which type. Read carefully.
SAT Pro Tip
For successive percentage changes, just multiply all the multipliers together. A 10% increase, then a 20% decrease, then a 15% increase: . That is a 1.2% net increase. Done in 5 seconds, no step-by-step needed.
Ready to master percentages? Try our Percentages lessons with practice exercises and hints.