Civil Services Prep

Prelims 2026 · CSAT / Quantitative Aptitude · Question 51

Seven cubes are identical in shape. Out of these, the weight of each of the six cubes is equal and the weight of the remaining cube is less than the weight of any other cube. A balance is used to identify the lightest cube. What is the minimum number of attempts required to distinguish the odd cube with certainty?<br/>

  1. 2
  2. 3
  3. 4
  4. 1

Answer

2

Use the balance as 3 vs 3.

  • If they balance, the 7th cube is the light one.
  • If not, the lighter side contains the odd cube among 3 cubes.
    Then weigh 1 vs 1 from those 3. If one side is lighter, that cube is odd; if they balance, the third cube is odd. So 2 weighings are sufficient, and 1 is impossible for 7 possibilities.
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