Because 15% of 100 is 15…

#TROY Just a newbie here, I have a question. If you have a currency and it loses -40%, you also lose -40% of its value, but it should recover -20%, the value should go up 20%, people say to buy in the red, like when I bought the currency it was 40% old, I put 100 BRL and then it was 15% green, I thought I would earn 55 BRL + the 100 but it didn't, lol