Two identical twins can only be distinguished by the characteristic that one always tells the truth and the other always lies. One twin tells you of a lucky number pair: "When I multiply my first lucky number by 3 and my second lucky number by 6, the addition of the resulting numbers produce a sum of 12. When I add my first lucky number and twice my second lucky number, the sum is 5." Which twin is talking? How do you know?
The first twin. The lucky numbers must be 2 and 1, respectively. The second twin is lying because 2+(1x2)= 4 not 5.
They are the liar. If 3x + 6y = 12, then x = 2 and y = 1. If x + 2y, then 2 + 2 would equal 4, not 5.