If we based solving this using the Central Limit Theorem, then if are given n random variables (in this case, losses from fire) and all with mean μ and standard deviation σ, then the distribution of the average of these random variables will behave in a normal distribution with mean μ and standard deviation σ /sqrt (n). Therefore the rules are:
μ’ = μ
σ’ = σ / sqrt (n)
So if we are given 10 policies, n = 10. Therefore the new
mean μ’ and standard deviation σ’ are:
μ’ = $300
σ’ = $400 / sqrt (10) = $126.49