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Variance and expectation

 
 
Reply Mon 10 Jan, 2011 08:49 am
A random variable X has expectation 35 and variance 25. Calculate expectation and standard deviation of the random variable Y=4X-20.

I'm searching for a step-by-step answer. Thank you very much for your help!
 
engineer
 
  3  
Reply Mon 10 Jan, 2011 08:53 am
@Schwermetall,
Expectation (or mean) of 4x-20 = 4*35 - 20 = 120
Std deviation of X is sqrt(25) = 5 ---- std deviation = sqrt(variance)
Std deviation of 4x-20 = 4*5 = 20 --- the bias (-20) doesn't change the std deviation
Schwermetall
 
  1  
Reply Mon 10 Jan, 2011 09:00 am
@engineer,
Thank you very, very much. :-) Couldn't set X and Y in relation somehow.
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