# Thread: [SOLVED] Random Variables

1. ## [SOLVED] Random Variables

The random variable T has the:
Mean 20
Standard deviation 5

It is required to scale T by using the transformation S = aT + b where a and b are constants ( a > 0 ) so that E ( S ) and Var ( S ) satisfy specified values.

Find the value of a and b in this particular case:

when E ( S ) = 0
and when Var ( S ) = 1

2. ## Try these numbers in your equations

Your original mean is 20. So subtract 20 from all the numbers to get a mean of 0.

Your original std deviation is 5, So scale by 1/5 to reduce the std deviation to 1.

These combine to a transformation of (1/5)x -20.

3. ## Random Variables

I see what you mean, but the transformation says + b, and you've used a minus (-20 ) =/

4. The standard language is such that +B means add some constant. There is no constraint that the constant be positive unless the language says "add a positive constant". So negatives are fine. In the future, you might have to add a complex number, which is neither positive nor negative.

5. ## Random Variables

that makes sense, i understandd now, thank you for the help