The joint probability function of two discrete random variable

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The joint probability function of two discrete random variable x and y given as
f_XY(x, y) = X + 2Y ; X = 0, 1
14
0; otherwise

then E [x]

1. 1
  7
2. 2
  7
3. 3
  7
4. 4
  7

Correct Option: D

	_∞	_∞
E[X] =			X.f _XY(x, y)
	^{X = – ∞}	^{Y = – ∞}

	₁	₂
=			x.	(X + 2Y)
	^{X = 0}	^{Y = 1}	x.	14

=	[1.(1 + 2) + 1.(1 + 4)]
	14

=	8
	14

=	4
	7