यदि X और Y दो यादृच्छिक चर हैं, जिनका घनत्व फलन 

f(x,y)={(6xy)8,0<x<2,2<y<4 0,elsewhere है, तो P(X + Y < 3) किसके बराबर है?

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SSC CGL Tier-II (JSO) 2022 Official Paper (Held On: 4 March 2023)
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  1. 324
  2. 124
  3. 38
  4. 58

Answer (Detailed Solution Below)

Option 2 : 124
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Detailed Solution

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सही विकल्प 2 है।

विस्तृत हल:

अवधारणा:

दो यादृच्छिक चर X और Y के संयुक्त संचयी फलन को इस प्रकार परिभाषित किया जाता है:

FXY=P(X<x,Y<y)

संयुक्त CDF निम्नलिखित गुणों को संतुष्ट करता है:

  • FX(y)=FXY(fty,Y), किसी भी y के लिए (Y का सीमांत CDF)
  • FX(x)=FXY(X,fty), किसी भी x के लिए (X का सीमांत CDF)
  • FXY(fty,fty)=1
  • FXY(x,fty)=FXY(fty,y)=0
  • P(x1 < X < x2, y1 < Y < y2) = FXY(x2, y2) - FXY(x1, y2) - FXY(x2, y1) + FXY(x1, y1
  • यदि X और Y स्वतंत्र हैं, तो FXY(x, y) = FXY(x) FXY(y) 

दो यादृच्छिक चर X और Y संयुक्त रूप से सतत हैं, यदि एक गैर-ऋणात्मक फलन fXY : ℝ2 → ℝ का अस्तित्व इस प्रकार है कि किसी भी समुच्चय A ∈ ℝ2 के लिए, हमें प्राप्त है:

P((X,Y)A)=AfXY(x,y)dxdy (5.15)

फलन fXY(x, y) को X और Y का संयुक्त प्रायिकता घनत्व फलन (PDF) कहा जाता है। सीमांत (PDF) 

fX(x)=fXY(x,y)dy, for all x

fY(y)=fXY(x,y)dy, for all y

गणना:

 f(x,y)={(6xy)8,0<x<2,2<y<4 0,elsewhere
 
qImage64a54439e3cc31bfce719c96
P(X + Y < 3) = ty=2y=4tx=0x=3yf(x,y)dxdy
 
P(X + Y < 3) = ty=2y=4tx=0x=3y((6xy)8)dxdy
P(X+Y<3)=y=2y=4x=0x=3y(6xy8)dxdy
=18y=2y=4x=0x=3y(6xy)dxdy
=18y=2y=4(6xx22xy)x=0x=3ydy
=18y=2y=4{6(3y)(3y)22(3y)y}dy
=18y=2y=4{(186y)(923y+y22)(3yy2)}dy
=18y=2y=4(2726y+y22)dy
=18{272y3y2+y36}y=2y=4
=18{272(42)3(164)+16(648)}
=18{2736+283}
=124
 
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