Amateurs have nine mice to go through. Start by putting three mice in each side of the scale, with three left over.
-- If one side weighs less, the light mouse is in that group of three.
-- If both sides weigh the same, the light mouse is in the last group of three, the ones you didn't weigh.
Remove all the mice except the group of three that has the light mouse in it. Of those three, put one in each pan and put the third one down with the others (but apart, so you can remember which one it is).
-- If one side weighs less, that's the light mouse.
-- If both sides weigh the same, the light mouse is the one you put down with the others.
