1. The problem statement, all variables and given/known data a memory stick was sold with 3 $ discount seven discounted memory sticks costed 12 dollars more than five of the non-discounted-memory sticks what is the price of non-discounted memory stick (normal price if you will) 2. Relevant equations 3. The attempt at a solution This is probably simple problem to most of you guys but I always had difficulty with this type of riddles. I dont think I ever got the reason why, why some constant value, should be added to either the left side of the equation or the right side of the equation. x = normal price in $ x-3 = discounted price, discounted by 3$ 7 * (x-3) = 5x I'm drawing a blank here... help me out heere. Something is twelve more or twelve less. 12 needs to be added or subtracted from something I think... Reasoning is below. But isn't the whole purpose of making an equation to say simply... the scale is now balanced. If the scale is balanced on both sides, then the equation is balanced and the equation has some real solutions. (I think) For inequalities, the purpose is that one side of the inequality is more than the other side.