Triangle Flash Cards are a fantastic way for students to practice fact fluency. These cards allow students to practice addition and subtraction facts at the same time. They also reinforce the idea that addition and subtraction are related operations.To use the flash cards, hide one of the corner numbers with a thumb or finger and have the student tell you what the hidden number is. For example, if the three corners contain an 8, a 2, and a 10 and the finger covers the 10, students would be expected to add 8 and 2 and state the hidden sum. If the 8 is covered, students would subtract 2 from 10 and state the hidden dividend.