Multiplication by 4.
Set up one 20-card deck of Power of Ten cards, stacked in a face-down pile.
1. The dealer turns over the top card from the deck.
2. The first player to say the correct answer to ‘double the double’
wins the card (this is the same as multiplying by four).
3. Another card is turned over and the process is repeated until all
cards have been turned over.
4. The player with the most cards at the end wins.