you can pay any amount you want as a fee for the transaction, this is called gas. your transaction goes on the ledger, the more gas you give it the more urgency it gets so the faster it gets processed.  in the old days you could send transactions with 0 gas, it would take months to get there but it'd get processed eventually, now days i don't think you can. crypto exchanges often have a set % for the gas fee, and they take their fee on top of that. exchanges normally figure out the gas price to pay based on time, they can figure out how much gas they need to give it to make the transaction happen in 5-10 minutes or less and pay that amount.
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