# [SOLVED] Mean and sd of transformation

• Oct 4th 2008, 09:28 AM
javs156
[SOLVED] Mean and sd of transformation
X is random variable with mean 44.584 and sd 89.265. What non zero value maust a take so that random variable given by Y=aX + a^2 has its mean equal to its sd?

I get 44.681 but am not sure if method is correct:

E(Y) = a*mean + a^2

V(Y) = a^2*sd^2

and then equate them.

Is this right?
• Oct 4th 2008, 02:58 PM
mr fantastic
Quote:

Originally Posted by javs156
X is random variable with mean 44.584 and sd 89.265. What non zero value maust a take so that random variable given by Y=aX + a^2 has its mean equal to its sd?

I get 44.681 but am not sure if method is correct:

E(Y) = a*mean + a^2

V(Y) = a^2*sd^2

and then equate them.

Is this right?

Your method is correct (provided mean and sd^2 refer to the random variable X). I haven't checked the arithmetic.
• Oct 5th 2008, 01:43 AM
javs156
would sum1 mind checking that the answer is correct?
• Oct 5th 2008, 05:39 AM
mr fantastic
Quote:

Originally Posted by javs156
would sum1 mind checking that the answer is correct?

It's easier (for me anyway) to check an answer (as opposed to validating a method) if the details of the calculation leading to the answer are given. Please keep that in mind for next time.