Here is market B:
I'm not sure I understand how this market works. I can only buy YES or NO. So if Market B resolves to 80%... how does Market A resolve?
The number of shares is equal to the Payout if YES / Payout if NO.
A resolution of 80% pays out M0.8 per YES share and M0.2 per NO share. The total payout is the same as the expectation at a probability of 80%. In other words, regardless of YES or NO, if you placed a bet at a probability of 80%, and it is resolved to a probability of 80%, your gain or loss is 0.