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GATE 2026 PI – Question 10

General Aptitude · Quantitative Aptitude: Data Interpretation, Arithmetic and Number Computation · 2 marks · Multiple choice

Positive integers P,Q satisfy $P^2=Q^2+13$. Find PQ.

  1. 13
  2. 26
  3. 39
  4. 42

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Show answer and explanation

Correct answer: (D) 42

Explanation

Factor $P^2-Q^2=(P-Q)(P+Q)=13$. Since 13 is prime and both factors are positive integers, $P-Q=1$ and $P+Q=13$. Thus P = 7, Q = 6, and **PQ = 42, D**.

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