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Official PYQ · 2011

GATE CS 2011 Q57 — General Aptitude

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If log⁡(P)=(1/2)log⁡(Q)=(1/3)log⁡(R)\log (\text{P}) = (1/2)\log (\text{Q}) = (1/3)\log (\text{R}), then which of the following options is TRUE?

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Answer: B

Let the given logarithmic relation be equal to a constant kk:

log⁡(P)=12log⁡(Q)=13log⁡(R)=k\log(P) = \frac{1}{2}\log(Q) = \frac{1}{3}\log(R) = k

Using the property of logarithms alog⁡(x)=log⁡(xa)a \log(x) = \log(x^a), we can rewrite the terms as:

log⁡(P)=log⁡(Q1/2)=log⁡(R1/3)=k\log(P) = \log\left(Q^{1/2}\right) = \log\left(R^{1/3}\right) = k

Taking the antilogarithm on all sides, we get:

P=Q1/2=R1/3P = Q^{1/2} = R^{1/3}

Now, we express QQ and RR in terms of PP:

  • Q=P2Q = P^2
  • R=P3R = P^3

Let's verify the given options using these relations:

  • Option A: P2=Q3R2  ⟹  P2=(P2)3(P3)2=P12P^2 = Q^3 R^2 \implies P^2 = (P^2)^3 (P^3)^2 = P^{12} (False)
  • Option B: Q2=PR  ⟹  (P2)2=P⋅P3  ⟹  P4=P4Q^2 = PR \implies (P^2)^2 = P \cdot P^3 \implies P^4 = P^4 (True)
  • Option C: Q2=R3P  ⟹  (P2)2=(P3)3⋅P  ⟹  P4=P10Q^2 = R^3 P \implies (P^2)^2 = (P^3)^3 \cdot P \implies P^4 = P^{10} (False)
  • Option D: R=P2Q2  ⟹  P3=P2(P2)2=P6R = P^2 Q^2 \implies P^3 = P^2 (P^2)^2 = P^6 (False)

Thus, the correct option is B.

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