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GATE 2014 EC (EC2) – Question 7

General Aptitude · Analytical Aptitude: Logical Reasoning and Deduction · 2 marks · Multiple choice

Each ladder step has two lights, chosen from red, blue, green and yellow. Whenever a light is red, the other on its step is blue. Whenever one is green, the other is yellow. Which statement is NOT necessarily correct?

  1. Number of red lights equals number of blue lights.
  2. Number of green lights equals number of yellow lights.
  3. Red plus green lights equals yellow plus blue lights.
  4. Red plus blue lights equals green plus yellow lights.

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Show answer and explanation

Correct answer: (D) Red plus blue lights equals green plus yellow lights.

Explanation

Under the intended two permitted pair types, each red light is paired with blue and each green with yellow. Hence R=B and G=Y, and consequently R+G=B+Y. However the number of red-blue pairs need not equal the number of green-yellow pairs. Thus **R+B=G+Y,D** is not necessary. The wording implicitly intends only these two pair types.