Raised of very interesting question:
https://coinmarketcap.com/ru/currencies/bitcoin/#markets the price is shown for bitcoin in dollars according to exchange and type of currency pairs and how in fact it is calculated? (for example, there is the couple of LTC/BTC for any exchange - how the bitcoin price in dollars is determined for this couple?)
So it's BTC price in USD times by the BTC price of the coin. And the way that they account for the different prices on all of the exchanges is just by taking an average. The only thing I am not sure of is if it is a weighted average (as in if one exchange has 80% of the volume then they do 0.8* that price and another exchange as 20% it's 0.2* that price and then they add the two together.