In this post about Slasher algorithm: https://blog.ethereum.org/2014/01/15/slasher-a-punitive-proof-of-stake-algorithm, it says:
At block K+1000, an address A with balance B gains a “signing privilege” if
sha256(n[K] + n[K+1] + ... + n[K+99] + A) < 2^256 * 64 * B / M.
Essentially, an address has a chance of gaining a signing privilege proportional to the amount of money that it has, and on average 64 signing privileges will be assigned each block.
How does this inequality ensures that on average 64 signing privileges will be assigned each block?