(10) Let X, Y be independent and let X ~ N(a1, b;) and let Y ~ N(a2, b;). Using the properties of mgf, if possible, prove that Z = X + Y is again a normal random variable. The following proofs are provided. (a) The statement of the exercise is, in fact, always false. (e) The statement of the exercise is true when aj = a2 and bi = b2. (e) From the table of mgfs we see that the mgfs of X and Y are Yx(t) = exp{(t –- a¡)²/2}, Yy(1) = exp{(t – a2)²/2}. By the convolution property, ¥z(t) = ¥x(t)Yy(1) = exp{(t – (a1 + az))²/2}. This is an mgf of a normal random variable. (d) From the table of mgfs we see that the mgfs of X and Y are Yx(t) = exp{r²/2}, ¥y(1) = exp{r²/2}. By the convolution property, ¥z(t) = ¥x(t)Yy(1) = exp{2r²/2}. This is an mgf of a normal random variable. te) From the table of mgfs we see that the mgfs of X and Y are ¥x(t) = exp{a¡t+ (b¡r²12)}, ¥y(1) = exp{azt + (b;r²/2)}. By the convolution property, ¥z(t) = ¥x(t)\Yy(t) = exp{(a, + a2)t + ((b² + - b²)r²12)}. This is an mgf of a N(a¡ + a2, (b² + b;)) random variable. (a) (b) (c) (d) (e) N/A (Select One)

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(10) Let X, Y be independent and let X ~ N(a1,b²)
and let Y ~ N(a2, b5). Using the properties of mgf, if possible, prove that Z = X + Y is again a normal random variable.
The following proofs are provided.
(a) The statement of the exercise is, in fact, always false.
(c) The statement of the exercise is true when a1 = a2 and b1 = b2 .
(c) From the table of mgfs we see that the mgfs of X and Y are
¥x(t) = exp{(t – aj)²/2},
¥y(t)
- exp{(t – a2)²/2}.
By the convolution property,
Yz(1) = ¥x(t)¥y(1) = exp{(t – (a1 + az))²/2}.
%3D
This is an mgf of a normal random variable.
(d) From the table of mgfs we see that the mgfs of
X and
Y
are
¥x(t) = exp{r?/2},
¥y(t) = exp{r²/2}.
By the convolution property,
Yz(t) = ¥x(t)¥y(t) = exp{2t²/2}.
%D
This is an mgf of a normal random variable.
(e) From the table of mgfs we see that the mgfs of X
and
Y are
Yx(t) = exp{a¡t+ (b;t2/2)},
Yy(t) = exp{azt + (b;t²/2)}.
By the convolution property,
Yz(1) = ¥x(t)¥y(1) = exp{(a1 + a2)t + ((b} + b})t² /2)}.
This is an mgf of a N(a1 + a2, (b; + b5)),
random variable.
(a)
(b)
(c)
(d)
(e)
N/A
(Select One)
Transcribed Image Text:(10) Let X, Y be independent and let X ~ N(a1,b²) and let Y ~ N(a2, b5). Using the properties of mgf, if possible, prove that Z = X + Y is again a normal random variable. The following proofs are provided. (a) The statement of the exercise is, in fact, always false. (c) The statement of the exercise is true when a1 = a2 and b1 = b2 . (c) From the table of mgfs we see that the mgfs of X and Y are ¥x(t) = exp{(t – aj)²/2}, ¥y(t) - exp{(t – a2)²/2}. By the convolution property, Yz(1) = ¥x(t)¥y(1) = exp{(t – (a1 + az))²/2}. %3D This is an mgf of a normal random variable. (d) From the table of mgfs we see that the mgfs of X and Y are ¥x(t) = exp{r?/2}, ¥y(t) = exp{r²/2}. By the convolution property, Yz(t) = ¥x(t)¥y(t) = exp{2t²/2}. %D This is an mgf of a normal random variable. (e) From the table of mgfs we see that the mgfs of X and Y are Yx(t) = exp{a¡t+ (b;t2/2)}, Yy(t) = exp{azt + (b;t²/2)}. By the convolution property, Yz(1) = ¥x(t)¥y(1) = exp{(a1 + a2)t + ((b} + b})t² /2)}. This is an mgf of a N(a1 + a2, (b; + b5)), random variable. (a) (b) (c) (d) (e) N/A (Select One)
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