A person having 100 million old coins after the exchange will receive 100,000 new coins is this normal? And most importantly, it is not clear how much new coins will cost
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It happens all the time... coins get redeveloped etc and have numbers reduced. Your new 100,000 coins will have the same value as your previous 100,000,000 because the market cap will remain the same.
Remember, value is just market cap divided by circulating supply. That means the new coins will be much more valued at $0.04 compared to the current cost of $0.00004 assuming market cap remains stable.