Uncle percy sold t-shirts at the show. now he only have 10% of the t-shirts he started with. if he has 25 t-shirts now, how many did he start with

Percy used to have 100% of the shirts (before he started selling them). Since then, he has given away 90% of the shirts and is now left with only 10% of what he used to have. He currently has 25 shirts, meaning that 25 is 10% of what he had.

Lets set up a proportion:

25 shirts : 10%
x shirts : 100%

x = 25*100 / 10
x = 2500 / 10
x = 250 shirts
Percy started off with 250 shirts.