Functions of random variables

Questions defining new random variables as functions of given ones (like Y = aX + b or Y = X²) and asking for their distributions, means, or variances.

3 questions

OCR S4 2017 June Q2
2 The independent discrete random variables \(X\) and \(Y\) can take the values 0,1 and 2 with probabilities as given in the tables.
\(x\)012
\(\mathrm { P } ( X = x )\)0.50.30.2
\(\quad\)
\(y\)012
\(\mathrm { P } ( Y = y )\)0.50.30.2
The random variables \(U\) and \(V\) are defined as follows: $$U = X Y , V = | X - Y | .$$
  1. In the Printed Answer Book complete the table giving the joint distribution of \(U\) and \(V\).
  2. Find \(\operatorname { Cov } ( U , V )\).
  3. Find \(\mathrm { P } ( U V = 0 \mid V = 2 )\).
Edexcel FS1 AS Specimen Q2
  1. The discrete random variable \(X\) has probability distribution given by
\(x\)- 10123
\(P ( X = x )\)\(c\)\(a\)\(a\)\(b\)\(c\)
The random variable \(Y = 2 - 5 X\)
Given that \(\mathrm { E } ( \mathrm { Y } ) = - 4\) and \(\mathrm { P } ( \mathrm { Y } \geqslant - 3 ) = 0.45\)
  1. find the probability distribution of X . Given also that \(\mathrm { E } \left( \mathrm { Y } ^ { 2 } \right) = 75\)
  2. find the exact value of \(\operatorname { Var } ( \mathrm { X } )\)
  3. Find \(\mathrm { P } ( \mathrm { Y } > \mathrm { X } )\) \section*{Q uestion 2 continued}
Edexcel FS1 2020 June Q4
  1. The discrete random variable \(X\) has the following probability distribution.
\(x\)- 5- 234
\(\mathrm { P } ( X = x )\)\(\frac { 1 } { 12 }\)\(\frac { 1 } { 6 }\)\(\frac { 1 } { 4 }\)\(\frac { 1 } { 2 }\)
  1. Find \(\operatorname { Var } ( X )\) The discrete random variable \(Y\) is defined in terms of the discrete random variable \(X\)
    When \(X\) is negative, \(Y = X ^ { 2 }\)
    When \(X\) is positive, \(Y = 3 X - 2\)
  2. Find \(\mathrm { P } ( Y < 9 )\)
  3. Find \(\mathrm { E } ( X Y )\)