Why do we need the expected value for calculating the variance in this task?
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I have a rectangle by sides $X$, $Y$ , $Z$. Where they also is independet stochastic variable with $E(X) =E(Y) =E(Z) =1cm$. $Var(X) = 0.5$ , $Var(Y) = Var(Z) = 0.75$. What is the variance for the box's volume?
…
I just don't get it. Why do we need $E(.)$ at all? When $Var(.)$ is already calculated? Why not just multiply all the $Var(.)$'s?
probability
asked Nov 16 at 13:26
soetirl13
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I have a rectangle by sides $X$, $Y$ , $Z$. Where they also is independet stochastic variable with $E(X) =E(Y) =E(Z) =1cm$. $Var(X) = 0.5$ , $Var(Y) = Var(Z) = 0.75$. What is the variance for the box's volume?
…
I just don't get it. Why do we need $E(.)$ at all? When $Var(.)$ is already calculated? Why not just multiply all the $Var(.)$'s?
probability
asked Nov 16 at 13:26
soetirl13
114
1
Because variance doesn't multiply: stats.stackexchange.com/a/52699
– K B Dave
Nov 16 at 13:31
add a comment |
up vote
0
down vote
favorite
up vote
0
down vote
favorite
I have a rectangle by sides $X$, $Y$ , $Z$. Where they also is independet stochastic variable with $E(X) =E(Y) =E(Z) =1cm$. $Var(X) = 0.5$ , $Var(Y) = Var(Z) = 0.75$. What is the variance for the box's volume?
…
I just don't get it. Why do we need $E(.)$ at all? When $Var(.)$ is already calculated? Why not just multiply all the $Var(.)$'s?
probability
asked Nov 16 at 13:26
soetirl13
114
I have a rectangle by sides $X$, $Y$ , $Z$. Where they also is independet stochastic variable with $E(X) =E(Y) =E(Z) =1cm$. $Var(X) = 0.5$ , $Var(Y) = Var(Z) = 0.75$. What is the variance for the box's volume?
…
I just don't get it. Why do we need $E(.)$ at all? When $Var(.)$ is already calculated? Why not just multiply all the $Var(.)$'s?
probability
probability
asked Nov 16 at 13:26
soetirl13
114
asked Nov 16 at 13:26
soetirl13
114
asked Nov 16 at 13:26
soetirl13
114
asked Nov 16 at 13:26
soetirl13
114
asked Nov 16 at 13:26
soetirl13
114
114
1
Because variance doesn't multiply: stats.stackexchange.com/a/52699
– K B Dave
Nov 16 at 13:31
add a comment |
1
Because variance doesn't multiply: stats.stackexchange.com/a/52699
– K B Dave
Nov 16 at 13:31
1
1
Because variance doesn't multiply: stats.stackexchange.com/a/52699
– K B Dave
Nov 16 at 13:31
Because variance doesn't multiply: stats.stackexchange.com/a/52699
– K B Dave
Nov 16 at 13:31
add a comment |
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Because variance doesn't multiply: stats.stackexchange.com/a/52699
– K B Dave
Nov 16 at 13:31