UPSC Prelims 2020·CSAT·Logical Reasoning·Deductive Logic

Three Statements S1, S2 and S3 are given below followed by a Question: S1: C is younger than D, but older than A and B. S2: D is the oldest. S3: A is older than B. Question: Who among A, B, C and D is the youngest? Which one of the following is correct in respect of the above Statements and the Question?

Dalvoy logo
Reviewed by Dalvoy
UPSC Civil Services preparation
Last updated 23 May 2026, 3:31 pm IST
  1. AS1 alone is sufficient to answer the Question
  2. BS1 and S2 together are sufficient to answer the Question
  3. CS2 and S3 together are sufficient to answer the Question
  4. DS1 and S3 together are sufficient to answer the Question.Correct

Explanation

Let's analyze the statements and the question: S1: C is younger than D, but older than A and B. This can be written as: D > C > A and D > C > B. From S1 alone, we know D is the oldest (or among the oldest) and C is older than A and B. However, we don't know the relative age of A and B. So, the youngest could be A or B. S1 alone is not sufficient. S2: D is the oldest. This means D > A, D > B, D > C. S2 alone doesn't give us any information about the relative ages of A, B, and C. So, S2 alone is not sufficient. S3: A is older than B. This means A > B. S3 alone only tells us about A and B, not C or D. So, S3 alone is not sufficient. Now let's evaluate the options: A) S1 alone is sufficient to answer the Question As explained above, S1 (D > C > A and D > C > B) doesn't tell us whether A or B is younger. So, A is incorrect. B) S1 and S2 together are sufficient to answer the Question S1: D > C > A and D > C > B S2: D is the oldest (confirms D is the oldest, but doesn't resolve A vs B) Combining S1 and S2 still leaves the ambiguity between A and B as the youngest. So, B is incorrect. C) S2 and S3 together are sufficient to answer the Question S2: D is the oldest. S3: A > B. These statements tell us D is the oldest and A is older than B, but they don't provide any information about C's age relative to A or B. C could be older than A, younger than B, or in between. So, C is incorrect. D) S1 and S3 together are sufficient to answer the Question. S1: D > C > A and D > C > B S3: A > B Let's combine these: From S1, we know C is older than A (C > A). From S1, we know C is older than B (C > B). From S3, we know A is older than B (A > B). Putting these together in order from oldest to youngest: We have D > C (from S1). We have C > A (from S1). We have A > B (from S3). Therefore, the complete order is D > C > A > B. From this combined order, B is clearly the youngest. Thus, S1 and S3 together are sufficient to answer the question. The final answer is D
Logical Reasoning: Three Statements S1, S2 and S3 are given below followed by a Question: S1: C is younger than D, but older than A and B.

Related questions

More UPSC Prelims practice from the same subject and topic.