UPSC Prelims 2026·CSAT·other·data sufficiency

Directions for the next 5 (five) items : Each item in this section contains a question followed by two statements. Answer each item using the following instructions and mark your response on the Answer Sheet accordingly. Question : If x, y and z are integers, each greater than 1, then is x a prime number? Statement I : xy² = 116 Statement II : xz = 261

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  1. ASelect this option if the question can be answered using one of these statements alone, but cannot be answered using other statementCorrect
  2. BSelect this option if the question can be answered using either statement alone
  3. CSelect this option if the question can be answered using both the statements together, but cannot be answered using either statement alone
  4. DSelect this option if the question cannot be answered even using any of the statements

Explanation

The correct answer is Option A. To determine whether x is a prime number, we evaluate each statement using prime factorization.

Why Option A is correct: Statement I: xy² = 116. The prime factorization of 116 is 29 × 2². The problem states that x and y are integers strictly greater than 1. This means y² must be a perfect square factor of 116 that is greater than 1. The only perfect square satisfying this condition is 4 (where y = 2). Consequently, x must be 116 ÷ 4 = 29. Because 29 is unambiguously a prime number, Statement I alone is sufficient to definitively answer the question "Yes."

Statement II: xz = 261. The prime factorization of 261 is 3² × 29. The integer factors of 261 greater than 1 are 3, 9, 29, and 87. Thus, x could be 3 or 29 (which are prime numbers), or it could be 9 or 87 (which are composite numbers). Because Statement II yields ambiguous results regarding whether x is prime, it is not sufficient on its own.

Why the other options are incorrect:

  • Option B: This is incorrect because Statement II cannot answer the question alone due to the multiple composite and prime possibilities for x.
  • Option C: This is incorrect because Statement I is fully sufficient on its own; combining the statements is mathematically unnecessary.
  • Option D: This is incorrect because Statement I successfully and independently provides a definitive answer to the question.

Takeaway: In Data Sufficiency questions involving integer multiplication, always find the prime factorization of the product. This reveals the exact mathematical constraints on the variables, especially when perfect squares are involved.

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