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how to justify the probability of a linear transformation of a event?


which rule can be used to compute the probability of $P a<Xleq b $?Derive the marginal probability function for XDeriving the formula for transforming random variablesProbability of an event to occurAbout the difference between “probability” and “probability mass function”How to calculate the probability of this normally distributed event?Probability of an event that has happened, to have happened in a specific time range?Find PMF, Expectation and Variance.Probability problem(pmf, avg value, var, allocation) : hitting an enemy until he diesBishop - Pattern Recognition & Machine Learning, Exercise 1.4Probability distribution vs. probability mass function / Probability density function terms: what's the difference













0












$begingroup$


I am confused when I trying to understand this discussion



I have already known



the probability of a linear function $Y = g(X) = aX + b$, where X is a random variable with a PMF P_X(x)



is



$$
P_Y(y) =
sumlimits_x P_X(x)
$$



how to justify the probability equation of a event like this?



$$
P(

X > a

) =
P(

dfracX-musigma >
dfraca-musigma)

)
$$










share|cite|improve this question









$endgroup$
















    0












    $begingroup$


    I am confused when I trying to understand this discussion



    I have already known



    the probability of a linear function $Y = g(X) = aX + b$, where X is a random variable with a PMF P_X(x)



    is



    $$
    P_Y(y) =
    sumlimits_x P_X(x)
    $$



    how to justify the probability equation of a event like this?



    $$
    P(

    X > a

    ) =
    P(

    dfracX-musigma >
    dfraca-musigma)

    )
    $$










    share|cite|improve this question









    $endgroup$














      0












      0








      0





      $begingroup$


      I am confused when I trying to understand this discussion



      I have already known



      the probability of a linear function $Y = g(X) = aX + b$, where X is a random variable with a PMF P_X(x)



      is



      $$
      P_Y(y) =
      sumlimits_x P_X(x)
      $$



      how to justify the probability equation of a event like this?



      $$
      P(

      X > a

      ) =
      P(

      dfracX-musigma >
      dfraca-musigma)

      )
      $$










      share|cite|improve this question









      $endgroup$




      I am confused when I trying to understand this discussion



      I have already known



      the probability of a linear function $Y = g(X) = aX + b$, where X is a random variable with a PMF P_X(x)



      is



      $$
      P_Y(y) =
      sumlimits_x P_X(x)
      $$



      how to justify the probability equation of a event like this?



      $$
      P(

      X > a

      ) =
      P(

      dfracX-musigma >
      dfraca-musigma)

      )
      $$







      probability






      share|cite|improve this question













      share|cite|improve this question











      share|cite|improve this question




      share|cite|improve this question










      asked Mar 22 at 8:57









      brennnbrennn

      132




      132




















          1 Answer
          1






          active

          oldest

          votes


















          1












          $begingroup$

          It is because of simple algebra (for $sigma > 0$): $$beginalign
          x>a &iff x-mu > a-mu \
          &iff fracx-musigma > fraca-musigma.
          endalign$$

          So $X> a$ occurs if and only if $leftfracX-musigma > fraca-musigmaright$ occurs. Thus the two probabilities are the same.






          share|cite|improve this answer









          $endgroup$












          • $begingroup$
            thanks, I helps. and would you please give a real life example to illustrate this transformation? i am having some difficulties to get a complete understanding of it.
            $endgroup$
            – brennn
            Mar 22 at 9:06







          • 1




            $begingroup$
            Maybe just consider some numbers. Imagine for now that $mu=0$. So you need to understand $x>aiff x/sigma > a/sigma$. Could you see why this would be true if $sigma =2$ for instance (so $x>a iff x/2 > a/2$)?
            $endgroup$
            – Minus One-Twelfth
            Mar 22 at 9:09










          • $begingroup$
            What is so difficult? All outcomes where $X>a$ are outcomes where $(X-mu)/sigma>(a-mu)/sigma$ because of the algebra: $x>aiff (x-b)/c>(a-b)/c$ (when $c>0$) $$omega:X(omega)>a=omega:(X(omega)-mu)/sigma=(a-mu)/sigma$$
            $endgroup$
            – Graham Kemp
            Mar 22 at 9:13












          Your Answer





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          1 Answer
          1






          active

          oldest

          votes








          1 Answer
          1






          active

          oldest

          votes









          active

          oldest

          votes






          active

          oldest

          votes









          1












          $begingroup$

          It is because of simple algebra (for $sigma > 0$): $$beginalign
          x>a &iff x-mu > a-mu \
          &iff fracx-musigma > fraca-musigma.
          endalign$$

          So $X> a$ occurs if and only if $leftfracX-musigma > fraca-musigmaright$ occurs. Thus the two probabilities are the same.






          share|cite|improve this answer









          $endgroup$












          • $begingroup$
            thanks, I helps. and would you please give a real life example to illustrate this transformation? i am having some difficulties to get a complete understanding of it.
            $endgroup$
            – brennn
            Mar 22 at 9:06







          • 1




            $begingroup$
            Maybe just consider some numbers. Imagine for now that $mu=0$. So you need to understand $x>aiff x/sigma > a/sigma$. Could you see why this would be true if $sigma =2$ for instance (so $x>a iff x/2 > a/2$)?
            $endgroup$
            – Minus One-Twelfth
            Mar 22 at 9:09










          • $begingroup$
            What is so difficult? All outcomes where $X>a$ are outcomes where $(X-mu)/sigma>(a-mu)/sigma$ because of the algebra: $x>aiff (x-b)/c>(a-b)/c$ (when $c>0$) $$omega:X(omega)>a=omega:(X(omega)-mu)/sigma=(a-mu)/sigma$$
            $endgroup$
            – Graham Kemp
            Mar 22 at 9:13
















          1












          $begingroup$

          It is because of simple algebra (for $sigma > 0$): $$beginalign
          x>a &iff x-mu > a-mu \
          &iff fracx-musigma > fraca-musigma.
          endalign$$

          So $X> a$ occurs if and only if $leftfracX-musigma > fraca-musigmaright$ occurs. Thus the two probabilities are the same.






          share|cite|improve this answer









          $endgroup$












          • $begingroup$
            thanks, I helps. and would you please give a real life example to illustrate this transformation? i am having some difficulties to get a complete understanding of it.
            $endgroup$
            – brennn
            Mar 22 at 9:06







          • 1




            $begingroup$
            Maybe just consider some numbers. Imagine for now that $mu=0$. So you need to understand $x>aiff x/sigma > a/sigma$. Could you see why this would be true if $sigma =2$ for instance (so $x>a iff x/2 > a/2$)?
            $endgroup$
            – Minus One-Twelfth
            Mar 22 at 9:09










          • $begingroup$
            What is so difficult? All outcomes where $X>a$ are outcomes where $(X-mu)/sigma>(a-mu)/sigma$ because of the algebra: $x>aiff (x-b)/c>(a-b)/c$ (when $c>0$) $$omega:X(omega)>a=omega:(X(omega)-mu)/sigma=(a-mu)/sigma$$
            $endgroup$
            – Graham Kemp
            Mar 22 at 9:13














          1












          1








          1





          $begingroup$

          It is because of simple algebra (for $sigma > 0$): $$beginalign
          x>a &iff x-mu > a-mu \
          &iff fracx-musigma > fraca-musigma.
          endalign$$

          So $X> a$ occurs if and only if $leftfracX-musigma > fraca-musigmaright$ occurs. Thus the two probabilities are the same.






          share|cite|improve this answer









          $endgroup$



          It is because of simple algebra (for $sigma > 0$): $$beginalign
          x>a &iff x-mu > a-mu \
          &iff fracx-musigma > fraca-musigma.
          endalign$$

          So $X> a$ occurs if and only if $leftfracX-musigma > fraca-musigmaright$ occurs. Thus the two probabilities are the same.







          share|cite|improve this answer












          share|cite|improve this answer



          share|cite|improve this answer










          answered Mar 22 at 9:02









          Minus One-TwelfthMinus One-Twelfth

          3,328413




          3,328413











          • $begingroup$
            thanks, I helps. and would you please give a real life example to illustrate this transformation? i am having some difficulties to get a complete understanding of it.
            $endgroup$
            – brennn
            Mar 22 at 9:06







          • 1




            $begingroup$
            Maybe just consider some numbers. Imagine for now that $mu=0$. So you need to understand $x>aiff x/sigma > a/sigma$. Could you see why this would be true if $sigma =2$ for instance (so $x>a iff x/2 > a/2$)?
            $endgroup$
            – Minus One-Twelfth
            Mar 22 at 9:09










          • $begingroup$
            What is so difficult? All outcomes where $X>a$ are outcomes where $(X-mu)/sigma>(a-mu)/sigma$ because of the algebra: $x>aiff (x-b)/c>(a-b)/c$ (when $c>0$) $$omega:X(omega)>a=omega:(X(omega)-mu)/sigma=(a-mu)/sigma$$
            $endgroup$
            – Graham Kemp
            Mar 22 at 9:13

















          • $begingroup$
            thanks, I helps. and would you please give a real life example to illustrate this transformation? i am having some difficulties to get a complete understanding of it.
            $endgroup$
            – brennn
            Mar 22 at 9:06







          • 1




            $begingroup$
            Maybe just consider some numbers. Imagine for now that $mu=0$. So you need to understand $x>aiff x/sigma > a/sigma$. Could you see why this would be true if $sigma =2$ for instance (so $x>a iff x/2 > a/2$)?
            $endgroup$
            – Minus One-Twelfth
            Mar 22 at 9:09










          • $begingroup$
            What is so difficult? All outcomes where $X>a$ are outcomes where $(X-mu)/sigma>(a-mu)/sigma$ because of the algebra: $x>aiff (x-b)/c>(a-b)/c$ (when $c>0$) $$omega:X(omega)>a=omega:(X(omega)-mu)/sigma=(a-mu)/sigma$$
            $endgroup$
            – Graham Kemp
            Mar 22 at 9:13
















          $begingroup$
          thanks, I helps. and would you please give a real life example to illustrate this transformation? i am having some difficulties to get a complete understanding of it.
          $endgroup$
          – brennn
          Mar 22 at 9:06





          $begingroup$
          thanks, I helps. and would you please give a real life example to illustrate this transformation? i am having some difficulties to get a complete understanding of it.
          $endgroup$
          – brennn
          Mar 22 at 9:06





          1




          1




          $begingroup$
          Maybe just consider some numbers. Imagine for now that $mu=0$. So you need to understand $x>aiff x/sigma > a/sigma$. Could you see why this would be true if $sigma =2$ for instance (so $x>a iff x/2 > a/2$)?
          $endgroup$
          – Minus One-Twelfth
          Mar 22 at 9:09




          $begingroup$
          Maybe just consider some numbers. Imagine for now that $mu=0$. So you need to understand $x>aiff x/sigma > a/sigma$. Could you see why this would be true if $sigma =2$ for instance (so $x>a iff x/2 > a/2$)?
          $endgroup$
          – Minus One-Twelfth
          Mar 22 at 9:09












          $begingroup$
          What is so difficult? All outcomes where $X>a$ are outcomes where $(X-mu)/sigma>(a-mu)/sigma$ because of the algebra: $x>aiff (x-b)/c>(a-b)/c$ (when $c>0$) $$omega:X(omega)>a=omega:(X(omega)-mu)/sigma=(a-mu)/sigma$$
          $endgroup$
          – Graham Kemp
          Mar 22 at 9:13





          $begingroup$
          What is so difficult? All outcomes where $X>a$ are outcomes where $(X-mu)/sigma>(a-mu)/sigma$ because of the algebra: $x>aiff (x-b)/c>(a-b)/c$ (when $c>0$) $$omega:X(omega)>a=omega:(X(omega)-mu)/sigma=(a-mu)/sigma$$
          $endgroup$
          – Graham Kemp
          Mar 22 at 9:13


















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