Exchanges that directly buy/sell from/to an user always buy low and sell high. Other exchanges just connect user's buy/sell call with that of another.

The exchange gets bitcoin from the fees they charge per buy and sell order in this case yobit charges 0.2% worth of fees even the percentage is low if you combine those fees itll gonna be big like the fee we use when we send btc.

something like yobit buys bitcoin in first place from another exchanger so they have some initial bankroll to start then they start their service, at least they should do it this way.

then they have more bitcoin from what they earn through fees and what they hold from user's investments.

yobit goes dry because they are not managing things correctly and they don't have enough trades daily.

Exchanges get Bitcoins by having people buy and sell on their site, or, if the site sells Bitcoin directly, chances are they buy it from other exchanges or also buy from their users, and take it and aim to sell it.

There is a lot of math and economic theories put into exchanges, and there are teams of people running them at all times.

i doubt that it is enough to have only 50 bitcoins for the very beginning of an exchange in my opinion because there might be people who would like to buy way more in the beginning

also the exchanges definitely buy their first bitcoins from other exchanges or just mine it for the start themselves though they most probably dont do that any more as mining isnt profitable

exchange get profit from fee of transaction and margin of trade altcoin and bitcoin,but so far i dont see yobit campaign wallet is dry,yobit have strong funds,they have so many users and also have dice game.

They either already have mined them back when they're so easy to get, but mostly exchanges get BTC from sellers. They pay actual fiat for the seller's coins, with a commission, then they would sell it to the buyer.

exchangers are a business just like any other business, so they need to have some kind of starting capital in the first place so they buy it somewhere and start with that. and from then on they will only survive on their investment (their exchanger is their investment) and earn through eachange and the fees.

On the other end of the trade is another bitcoin user who wants to sell bitcoin, i thought this was basic economics