[pistol]

KOC's friend is the owner of a golf shop. Each box of Pro V is at cost of $250. And after a profit of $70 added onto it, each box of Pro V is sold at $320. So one day, a customer came in to buy a box, and handed the owner a $500 dollar bill. The owner just went out of change, and had to go over to his neighbor to change the 500 dollar bill into bills of different denominations. So after giving the customer the change, and the customer left, the neighbor came and claimed that the $500 dollar bill was fake. So the owner had to give the neighbor another $500 dollar bill to settle the dispute.

The question is: how much money KOC's friend lost at the end of the day?

$430 , if you want to count lost potential profit of $70 on that particular box of balls , then its $500