Three-Corner Flash Cards: Addition and Subtraction Go to amazon.com Related posts Top recommendation for solo 3 decade Feature48 Two-sided triangle cardsTeaches addition and subtraction and the relationship between themIdeal for 1st Grade to 3rd GradeAges 6 to 8 DescriptionThese flash cards are easy to hold and simple to use. Review facts 1 through 12 quickly. The flash cards are white in color.