Divide and conquer

Steps

1. Lay out the 15 cards in order. Tell the children the numbers go from small to large.
2. Ask them to find 52 by turning over as few cards as possible.
3. Start in the middle. If the number is too small, the card you want is to the right. If too big, to the left.
4. Throw away half the cards and look at the middle of what is left.
5. Count the guesses with the class. It is only a few.
6. Try other targets. Compare with last time, when the cards were not in order.

Talk about it

• Why does sorting help?
• What would you do with 100 cards?
• What if the number is not in the list?