# Thread: Mean/variance of random variable...hmmmm

1. ## Mean/variance of random variable...hmmmm

So here is the problem:

" The mean of a random variable, x, is 19 and its variance is 5. What is the mean, variance and standard deviation of y where y=7x-2? "

I'm new to random variable statistics, so I'm having trouble understanding how a variable x can have a mean and a variance...

Thanks!

2. Originally Posted by trank31337
So here is the problem:

" The mean of a random variable, x, is 19 and its variance is 5. What is the mean, variance and standard deviation of y where y=7x-2? "

I'm new to random variable statistics, so I'm having trouble understanding how a variable x can have a mean and a variance...

Thanks!
If the random variable X has mean $\displaystyle \mu$ and variance $\displaystyle \sigma^2$, then the random variable Y = aX + b has mean $\displaystyle a \mu + b$, variance $\displaystyle a^2 \sigma^2$ and standard deviation $\displaystyle |a| \sigma$.

In your question a = 7 and b = -2.