Consider the following two cases:
(1) 2-deck, bet spread 1-5;
(2) 8-deck, bet spread 1-10.
Let's assume that the expectation of the two cases are the same. (Well, you may argue that their expectation may not be exactly the same. To remedy this, we change the bet spread of 8-deck to whatever is needed to make the two cases the same expectation.)
My question is: which one has a higher variance? Please present your reasoning. Thanks.