Variance of a compound daily total

The number of trades you fill in a day is Poisson with mean 55. Each trade's size is independently equally likely to be 11, 22, or 33 lots, independent of how many trades there are. What is the variance of your total daily volume (in lots2^2)? Give a decimal to four places.

Show hints (2)+
  1. A random number of random sizes - use the law of total variance.
  2. For a Poisson count, Var⁡(S)=λE[X2]\operatorname{Var}(S)=\lambda E[X^2].

Answer

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23.3333 (± 0.01)

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