Double-Value Vertical Flash Cards - Addition & Subtraction Set - 90 Per Pack, 2 PacksNotched corners for quick organization. Large, easy to handle 6 1 4" x 3 1 4" cards. Bold, heavy type to use with large groups. Durable, thick card stock (14 pt.). Self checking. Great for small groups, pairs, and whole class participation. Great for teaching the relationship between + , (e. g.: 3+1=4 on one side, 4 1=3 on the reverse). Each set includes 90 cards. Sold as 2 sets for a total of 180 cards. Recommended age 5 8 years