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GATE 2023 ST – Question 19

Joint Distributions · Joint and Conditional Distributions · 1 mark · Multiple choice

The joint density is f(x,y)=8xy for 0<x<y<1,zero otherwise. If E(X | Y=y₀)=1/2,find y₀.

  1. 3/4
  2. 1/2
  3. 1/3
  4. 2/3

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Correct answer: (A) 3/4

Explanation

Integrating x from 0 to y gives f_Y(y)=4y³. Thus f_(X|Y)(x|y)=2x/y² on (0,y),whose mean is ∫₀ʸ2x²/y² dx=2y/3. Set this equal to 1/2 to get **y₀=3/4, A**.

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