When teaching multiplicative and additive comparisons using equations, should I leave the problems like this: 10 + y = 20 Missing an addend, so we should subtract 10 from 20 to find the missing addend. 10 x y = 20 Missing a factor, so we should divide 20 by 10 to solve for the missing factor. OR Should I show them how to isolate the variable. My kids will get the first way no problem because I have hammered that subtraction is inverse of addition, occurs when we are missing an addend, and division is inverse of multiplication--use when missing a factor. I'm thinking isolating variables is more middle school-ish, not elementary-ish? I can't find in my curriculum map anything about isolating variables--but I don't want that to show up the EOG having not shown them.