There was this exercice asking to compute several things, and the first results I got(varX, VarY, Cov) are okay, the same as the book.Then the book goes on asking he var of a linear function Here is my problem:
Given var(X)=var(Y)= 0.24 and Cov(X,Y)=-0.24
given W= 2X- 4Y compute Var(W)
Var(W)= 2^2 * var(X) + (-4)^2*var(Y) + 2*2*(-4)*Cov(X,Y)
and came up with= 8.64
but on the book the result is 0.48. Is there a mistake?