These cards include the number 21 - 40 with the Spanish written below the number, as well as cards without the Spanish words. You can practice with the Spanish set and then quiz with the set that doesn't have the Spanish words.
They are color coded. Every three numbers share a color and different shade, then this is repeated as you go higher. For example, 21-22-23 are all blue starting from light to dark, then 21-32-33 have the same shades. This is to add an extra sensorial dimension so the child can more easily recall the numbers.
My students had already learned 1 - 20 with the other set on my site. http://www.teacherspayteachers.com/Product/Spanish-Numbers-Flashcards-1434557 Once we incorporated 21 - 40, we were able to play more memory games and competition games.