I'm having trouble understanding the logic behind this puzzle - even in the hint, it says the camera price is $290, yet the answer for the puzzle is 95 This all makes zero sense to me!
Well, I'm talking on top of my head now, but here goes: The price of case: x The price of camera: x + $300 The camera price is $300 higher than the price of the case, therefore, altogether: x + x + $300 = $310 Now, some simple maths: 2x + $300 = $310 2x = $310 - $300 2x = $10 / :2 x = $5 The price of the case equals x, therefore it costs five dollars. You paid with a $100 banknote and must receive $95 of change. EDIT: I never bought any hints here, so I wouldn't know. But the price of the camera is definitely $305.
Step 1: you know it's not going to be $10, because that would be too easy and then it wouldn't be a puzzle. Step 2: Assume that the case were $10. The wording says "the camera costs $300 more than the case itself". So that would make the camera alone $310, so camera + case would be $320. Step 3: Since that's clearly too high, your next bet would be to reduce the price of the case as MaHe pointed out. Plug in $5, now the camera becomes $5+$300=$305. Add the case and you've got your $310. Step 4: The answer is how much change, so subtract that $5 from $100. Pretty easy overall.