It takes on average (difficulty)*2^32 hashes to solve a block.
A block is worth the block reward (currently 50 BTC + <1 BTC in tx fees.
Thus avg hashes per 1 BTC = (difficulty)*2^32 / 50 BTC.
You can't compare MH/s (which is a rate, MegaHashes per second) to BTC (which is a fixed amount).
One involves time. You can multiply MH/s by 1 second and get hashes in a second and thus the BTC in a second.
More usefully you can take the MH/s * 60*60 * 24 to get the hashes in one day and then determine the avg BTC earned in one day.
Your accurate math strains my brain
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