Edexcel 4MA1 Ratio & Percentage: Avoid These Mistakes

Ratio and percentage questions look easy — but they hide common traps.
Use this checklist to protect your marks.

Mistake 1: Not simplifying the ratio first

Always simplify before you calculate.
Example: 12:18 → 2:3.

Mistake 2: Mixing ratio and fraction language

If a part is “2 of 5,” that is 2/5 of the total.
Make the fraction explicit before calculating.

Mistake 3: Percentage of a percentage

When a value changes by a percent, apply the change to the current value, not the original.

Mistake 4: Reverse percentage problems

If something is “after” a change, you need to divide by the multiplier.
Example: 80% of original → divide by 0.8.

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