Help students develop addition skills by learning how to quickly add long strings of one-digit numbers. This can be a useful and fun skill for students of any age or skill level. Included is a lesson overview, printable worksheet with answer key and colorful slides to show in the classroom. Complements of 10 are two numbers that add up to 10, such as 1 and 9 2 and 8 3 and 7 4 and 6 and so on...