My question concerns the valuation of currencies (specifically cryptocurrencies such as bitcoin).

I understand that at any given point there may be people looking to sell currencies, the lowest of which is the bid price. Likewise, people looking to buy currency will also place an offer of which the highest is the ask price.

• Is the price of the currency (as we see it in charts) simply the average of the ask and bid prices?
• If the ask price is 100 and my bid is 99, then there will be no sale. If they both are 100, then there is; but what if my bid is higher than the ask price? What will happen, at what price is the currency sold and to whom goes the "left-over"?