60-second revision
- You judge whether the data is enough to answer — you do not need the final value.
- Test I alone, then II alone, and only if both fail, test them together.
- If I alone and II alone each work, the answer is 'either', not 'both'.
- A definite 'no' to a yes/no question is sufficient data.
- Never use outside assumptions; use only the facts in the question and statements.
- n independent equations are needed for n unknowns; a ratio alone never gives an actual value.
- If the data leaves two or more possible answers, it is not sufficient.
The answer choices
A data sufficiency question asks something and gives two statements. You must decide which statements are needed to answer it. The five standard choices are fixed; learn them so you do not waste time reading them in the exam. In this quiz each question shows four of the five.
| Choice | Meaning |
|---|---|
| I alone | Statement I answers it; II does not |
| II alone | Statement II answers it; I does not |
| Either | I alone answers it, and II alone also answers it |
| Both together | Neither alone answers it, but I and II together do |
| Neither | Even I and II together cannot answer it |
The routine
- Read the question and note exactly what is asked (a value, a relation, a yes/no).
- Cover II and test I alone. Can it give exactly one answer?
- Cover I and test II alone. Forget everything I said.
- If both failed, combine them and test again.
- Choose the option that matches your three results.
Reasoning DS
Reasoning DS questions use the topics you already know: blood relations, directions, ranking, days and dates, coding and arrangements. For each statement, quickly build the partial diagram and ask whether the asked item is fixed. Partial information that leaves two possibilities is not sufficient.
Worked example: 'Who is the tallest among A, B, C and D? I. A is taller than B and C. II. D is shorter than C.' I alone leaves A or D. II alone says nothing about A or B. Together, D < C < A and B < A, so A is the tallest — both statements are needed.
Quant DS
| Situation | Usually sufficient? |
|---|---|
| Two independent linear equations in two unknowns | Yes |
| One equation in two unknowns | No (unless the question asks for that exact combination) |
| Ratio of two quantities only | No actual values |
| Ratio plus the sum or difference | Yes |
| Simple interest: any three of P, R, T, SI (or amount) | Yes — the fourth follows |
| Rectangle: perimeter and diagonal | Yes — area = ((perimeter ÷ 2)² - diagonal²) ÷ 2 |
Worked example: 'What is the speed of a train? I. It crosses a pole in 12 seconds. II. It crosses a 240 m platform in 20 seconds.' I gives L = 12v, II gives L + 240 = 20v. Each has two unknowns, but together 12v + 240 = 20v, so v = 30 m/s. Both are needed.
Yes/no questions
When the question asks 'Is x even?' or 'Is A the brother of B?', a statement is sufficient if it gives a definite answer, whether that answer is yes or no. It is insufficient only if it allows both yes and no.
Test yourself: 10 questions, 60 s each
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