A random variable X has a mean of 120 and a standard deviation of 15. A random variable Y has a mean
 of 100 and a standard deviation of 9. If X and Y are independent, approximately what is the standard deviation of X - Y?
Added by Heather R.
Step 1
Variance(X - Y) = Variance(X) + Variance(Y) Variance(X - Y) = 144 + 81 Variance(X - Y) = 225 Show more…
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