UPSC Prelims 2010·GS1·science-and-technology·science and technology

A question paper had ten questions. Each question could only be answered as True (T) or False (F). Each candidate answered all the questions. Yet, no two candidates wrote the answers in an identical sequence. How many different sequences of answers are possible?

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Last updated 23 May 2026, 3:31 pm IST
  1. A20
  2. B40
  3. C512
  4. D1024Correct

Explanation

The problem asks for the total number of possible sequences for ten questions, where each question has two choices, True or False. This is a fundamental principle of counting. For each individual question, there are 2 possible outcomes. Since there are 10 questions and each is independent of the others, we multiply the number of choices for each question together. The calculation is 2 multiplied by itself 10 times, which is 2 raised to the power of 10. 2 x 2 x 2 x 2 x 2 x 2 x 2 x 2 x 2 x 2 equals 1024. Therefore, there are 1024 different possible sequences of answers. Since no two candidates wrote identical sequences, this is the maximum number of unique answer keys possible. The correct option is D.
science-and-technology: A question paper had ten questions. Each question could only be answered as True (T) or False (F). Each candidate answer

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