Maria and Cassie were playing a card game with the four cards below.
All the cards have a picture on one side and a number on the other side. Maria observed, "I think if a card has a bear on one side, then it has an even number on the other side."
Cassie paused, "I'm not sure that is true, but let's turn all the cards over and see."
Maria said, "We don't have to turn all the cards over. Let's use logic to figure out which cards we should turn over to help us."
Which cards do they have to turn over before they know if the rule is correct?