Proof of work: average number of tries to create a block First, I'm sorry if I'm asking a stupid question. I'm just trying to understand bitcoin. I'm reading the Ethereum white paper, and I couldn't understand this sentence about proof of work:


  At the current target of ~2^187, the network must make an average of
  ~2^69 tries before a valid block is found


My question: how the 2^69 number of tries is computed?



Updated:

My question: why 2^69 instead of 2^70 or 2^169?
As MeshCollider's comment mentions, it is simply the difference between the total number of bits against the target bits.

As to why it is this way is just a function of probability. If you have a range of 1-100, and your target is &lt;= 20, there are 20 numbers that satisfy your requirement. Thus, 20 * 1/100, or 20 tries out of 100 should result in a valid  number against your target.

It works the same way, although on a much larger scale here. Your target and attempt are both 256 bits numbers, which means they range from 0 to 2^256-1. If your target is 2^179, it means that 256-179, or 2^67 tries will, on average, produce a valid number against the target.