Tavadi

Damn! I just graduated from Physics and Mathematics School and Im still confused!

So I was reading editors manual and Im pretty confused about following sentence: 'However, operations are done from right to left, instead of the usual left to right (so 9 – 3 – 3 is 0, not 3, because the subtraction on the right is done first).' Ok dont tell me why its right to left, lets leave it, but HOW is '9 – 3 – 3 = 0'?? Please someone explain to me.