Tap a space that's in the minority. It will reverse relative to the rest. So if there are more checks them empties, tap an empty. If there are more empties, tap

Tap a space that's in the minority. It will reverse relative to the rest. So if there are more checks them empties, tap an empty. If there are more empties, tap a check. Eventually you have all but one boxes checked. Tap the empty box and the checks will clear.