Aptitude · Logical reasoning
Data sufficiency, made easy
💡 The idea
You do not need the answer, only whether you could find one exact answer. Test I alone, II alone, then both together.
I alone?→II alone?→Both?→Pick the option
🧭 The method: 3 steps
- Cover II and test I alone; then cover I and test II alone.
- Only if neither works alone, use both together.
- Two possible answers (like x = 7 or −7) means NOT enough.
🎬 Every kind of question, in pictures
Pick a kind. Guess the answer first, then watch the picture work it out. Tap any step to see it in the picture.
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✏️ Worked examples
Example 1. What is x? I: x + y = 10. II: x − y = 2.
- I alone: two unknowns
- II alone: two unknowns
- Together: 2x = 12
⚡ Shortcut: Both together are needed
⚠️ Where people go wrong
- Carrying facts from statement I into II when testing alone.
- Doing the full sum when you only need to know it is possible.
- Forgetting a square can be negative or positive.
📌 Remember
- I alone → II alone → both
- One exact answer = enough
- Comparisons alone rarely give values