Solution Step 0/0
Place 6 glasses on a table - 3 up, 3 down. Take any pair of glasses and invert them. If you continue to invert the pairs as long as you like, will you ever end up with all six glasses upright?
Explanations
The parity of the initial setup is odd. These are three pairs of one-up-one-down glasses as is shown in the diagram. An even number of moves won't change that.Therefore, all-upright glasses are impossible. Either all-inverted glasses, btw.
Check With odd moves
Check With even moves
Check Impossible
Check Partly possible
