UPSC Prelims 2015 CSAT Paper II · Q9 of 74 Basic Numeracy easy

Twelve people form a club. By picking lots, one of them will host a dinner for all once in a month. The number of dinners a particular member has to host in one year is

  1. (a) One
  2. (b) Zero
  3. (c) Three
  4. (d) Cannot be predicted ✓ UPSC's answer

Why the answer is (d)

• The problem states that the host is selected by 'picking lots' (random selection) each month, not by a fixed rotation.

• Since the selection is random, any specific member has a probability of being chosen in any given month, but it is not guaranteed.

• Over the course of 12 months, a particular member could be selected 0 times, 1 time, or multiple times.

• Because the outcome depends on chance and is not deterministic, the exact number of dinners a specific member will host cannot be calculated with certainty.

• Therefore, the number of dinners a particular member has to host is unpredictable.

Why the other options are wrong

(a) One
This assumes a fixed rotation where each member hosts exactly once a year, which contradicts the 'picking lots' (random) method.
(b) Zero
This assumes a specific member will never be selected, which is statistically possible but not a guaranteed outcome of random selection.
(c) Three
This assumes a specific frequency (3 times) without any basis in the random selection process described.

Asked in the CSAT Paper II of the UPSC Civil Services Preliminary Examination 2015, held on 23 August 2015. Question and answer key: Union Public Service Commission. Explanation: UPSC Answer Check.

Reading the answer is not the same as getting it right under a clock. Practise this question with UPSC's negative marking, and anything you miss goes into an error notebook until you get it right twice.

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