Can you buy some percent of bitcoin at different rates and merge them to form one bitcoin? Is it like you buy at different rates so you will get different exchange rates for particular percent
Buying bitcoin is no different to buying carrots.
If you buy 10kg of carrots for $3 in one place and the next day buy another 10kg of carrots for $4 you have 20kg of carrots.
Can you buy some percent of bitcoin at different rates and merge them to form one bitcoin?
Yes you can totally take your carrots out of your two 10kg bags of carrots and put all your carrots into one bag that then weighs 20kg.
Is it like you buy at different rates so you will get different exchange rates for particular percent
If you buy from a supermarket that only sells carrots in 10Kg bags, you likely wont be able to negotiate a bulk discount for buying one ton of carrots.
In the world of currency this is probably more true, the exchange rate probably varies less by transaction amount because your purchase is generally going to be tiny compared to market volume. But this is still a question about markets - not some weird voodoo that only applies to currencies.
The next day If someone is willing to pay you $0.40 a kg for your carrots you have $8 worth of carrots, not $7 worth of carrots.
The price of fresh carrots does not depend on what you paid for them, only on what people are willing to pay you for yours.
The point is that carrots are carrots, they are not some strange form of promises of future dollar amounts. They are not derivatives of dollars. They are carrots.