I believe I read all the responses, so now you get mine.
The young man resented being told he was wrong, and probably expected he was wrong, before being told. (someowne else with a bad taste)
This is what I would have done, and have done when mistakes are made by a younger person.(Try to find a way to help if the problem comes up again, politely.) Thank you for making all the cuts, so now lets see if we can find a way to make all these different sizes of cuts, and prices come together. And believe me I know fractions are difficult (He's thinking that "old woman"!!)
Take a piece of paper and start with one fabric. Sort any that are the same price to work side by side. Do each fabric, until all are written down.
When the operation if finished, tell him Quilters have to figure fractions all the time so after awhile the nasty process becomes second nature. And try to figure out a chart for him for
all fractions he's going to have to figure with fabric. And the chart will help all the clerks, and he can be the HERO. Keep on Quilting---CECELIA