But not the other.
Its doing my head in. I got the problems from Khan Academy, but they weren't explained in the video or on the practice page. I don't understand the difference?
the second question I would like to ask, is they have multiple choice selections, but in the answers they sometimes switch the variables around, and it has made me select the none of the above option. I always thought the answer was 2a + 2b - 4 is the answer not 2b +2a -4 , but quite often they have them the other way around, I guess thats one of the reasons I hate multiple choice. I'd rather just collect the answer for myself.