so if you bought 2 earbuds, you pay 25 (buy one get one free)
then you sell each for 17
so 17*2=34
spent 25
earned-spent=profit
34-25=9
he saves $25 since he doesn't have to pay for the second pair
cost for each pair is $25
profit for each pair is $9
he saves $25 off retail per pair
