I occasionally buy USD to load a prepaid debit card to buy things from online. My local currency is different (lets assume that my local currency name is 'A') and the amount and buying rate vary every time, naturally. Now some of my friends want me to buy some items for them using the debit card, what should be the ideal exchange rate if I don't want to profit or lose?
Lets say here's my buying history to load the debit card over time:
- 500 USD @ 1 USD = 10 'A' rate
- 300 USD @ 1 USD = 10.5 'A' rate
- 400 USD @ 1 USD = 11.1 'A' rate
Now if at any point someone ask for 600 USD to buy something, what should be the exchange rate? How do I calculate that?