Typically a good strategy is to solve a simplified version and generalize. In this case, assume only 1 card is face up. Take a single card from the deck:

Typically a good strategy is to solve a simplified version and generalize. In this case, assume only 1 card is face up. Take a single card from the deck: - if it was face up & you flip it, both have zero - if it was face down & you flip, both have one