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GATE 2023 ST – Question 55

Joint Distributions · Functions of Random Vectors · 2 marks · Multiple select

U,V are iid with density λ²x e^(−λx),x>0,λ>0. Which statements hold?

  1. U−V has a distribution symmetric about zero.
  2. The distribution of UV does not depend on λ.
  3. The distribution of U/V does not depend on λ.
  4. U/V has a distribution symmetric about 1.

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Show answer and explanation

Correct answer: (A) U−V has a distribution symmetric about zero.; (C) The distribution of U/V does not depend on λ.

Explanation

Exchangeability gives U−V equal in law to V−U,proving A. Write U=U₀/λ,V=V₀/λ with iid Gamma(2,rate 1). Their product scales by λ⁻²,whereas their ratio cancels λ,proving C. The positive ratio has unbounded support and cannot be additively symmetric about 1; reciprocal symmetry is different. **A,C**.

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