How easy it is to add three numbers such that their addition matches a certain number? That's the simplest rule underlying this game. Under a given time constraint, you are asked to pick 3, 4 or 5 tiles such that the combined face numbers match a certain number. So the combination of which numbers can make, say, 15? Well, it sounds easy. But what if the target number is 138? Can you pick 3, 4 or 5 tiles quickly?