Data sufficiency

Story hook

A CSAT question reads:

"What is x's age?" Statement I: x is 3 years older than y. Statement II: y is 18.

The candidate panics — neither statement alone solves it. But both together do: x = 18 + 3 = 21.

Then a different question:

"What is x's age?" Statement I: x is twice as old as y. Statement II: y will be 30 in 5 years.

Statement I alone: x = 2y (need y). Statement II alone: y = 25 (now). Doesn't give x. Both together: x = 50.

Notice: You never actually compute the answer in Data Sufficiency. You only decide whether the data is enough.

This is the most counter-intuitive section in CSAT. Once the structure is clear, every DS question is a 20-second decision tree.

Why this matters for UPSC

For CSAT (Paper II, qualifying 33%):

• 3-5 questions per paper are Data Sufficiency.
• DS is uniquely cognitive — tests logical thinking, not arithmetic.
• Real-life: Bureaucratic decisions are constantly DS-like — "Do I have enough info to act?" vs "Do I need more data?"

DS is fast if you understand the pattern. The trick is to NOT solve — just to decide.