Eliminate memory overload and learn 4 math facts on each side of a card! Triangle Flash Cards teach families of facts, showing the relationship between addition and subtraction. How is 4 in one corner related to 7 and 3 in the other corners? Cover the sum, in red, and practice addition: 4 + 3 = 7 or 3 + 4 = 7. Cover one of the addends, in black, and practice subtraction: 7 ? 4 = 3 or 7 ? 3 = 4. A total of 20 cards aid mastery of 160 math facts up to 9 + 9 and 18 - 9. Also available for multiplication and division. For 2 or more players. Bundle of 3 packs.