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UPSC Prelims 2026 CSAT, question 67

Topic: Logical reasoning

Q67

If ZERO is encoded as ADSN, then how do you encode STOP?

  1. (a) SPOT
  2. (b) TSPOCorrect answer
  3. (c) TSOP
  4. (d) POST

Solution.

Answer: (b) TSPO

  1. Comparing ZERO with ADSN letter by letter gives the alternating shift rule (+1,−1,+1,−1)(+1, -1, +1, -1): Z→+1A\text{Z} \xrightarrow{+1} \text{A}, E→−1D\text{E} \xrightarrow{-1} \text{D}, R→+1S\text{R} \xrightarrow{+1} \text{S}, and O→−1N\text{O} \xrightarrow{-1} \text{N}.
  2. Applying (+1,−1,+1,−1)(+1, -1, +1, -1) to STOP gives S→+1T\text{S} \xrightarrow{+1} \text{T}, T→−1S\text{T} \xrightarrow{-1} \text{S}, O→+1P\text{O} \xrightarrow{+1} \text{P}, and P→−1O\text{P} \xrightarrow{-1} \text{O}, which forms TSPO.