Okay, so im doing an Ixl on experimental probability. Everything was going fine, until i started getting questions wrong for adding when i wasn't supposed to. But keep in mind here there isn't exactly a plus sign telling you when to add. Apparently, your supposed to go off of your head. But it doesn't make sense to me, because i get questions wrong and on Ixl it takes you from a 80 to a 78 just for getting one question wrong. My teacher said I have to get at least 90. To make it even worse, im on a time crunch because im trying to finish the school year (its the last week of school) with honor roll like I do every semester. So my question is:
How do you know when to add for experimental probability?