Variance of a weighted dice combination

Two fair dice are rolled independently, giving $X_1$ and $X_2$ . What is the variance of the combination $X_1 + 2X_2$ ? (to 2 decimals)

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Independence lets the variances add: Var(X1) + Var(2 X2).
A multiplier c scales variance by c^2, so Var(2 X2) = 4 Var(die); one die has variance 35/12.

Answer

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14.58 (± 0.01)

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Asked at: Timed Mental-Math & Sequences, Game-Based Aptitude