Data Sufficiency: Percentage-based Sufficiency

Concept Explanation

Percentage DS items test whether you can find a unique percent, part, or whole—watch the base of every percentage.

Standard Answer Choices

• A — Statement I alone is sufficient; Statement II alone is not.
• B — Statement II alone is sufficient; Statement I alone is not.
• C — Both together are sufficient, neither alone.
• D — Either statement alone is sufficient.
• E — Neither alone nor together is sufficient.

Percentage DS Focus

Identify whether the question asks for x% of N, what percent one value is of another, or increase/decrease on an original base.

DS Decision Flow

1. State exactly what must be determined (number, ratio, yes/no, or comparison).
2. Test Statement I alone—sufficient or insufficient?
3. Test Statement II alone—sufficient or insufficient?
4. If neither alone works, combine both statements.
5. Choose A–E based on sufficiency; never pick a value when data do not fix it uniquely.

Common Traps in Percentage Problems

• Applying successive changes on the wrong base.
• Assuming part and whole when only one is given.
• Mixing percentage points with percentage change.