Adding and subtracting 10 is easy once you understand the tricks! Learners first write numbers that are ten more than two double-digit numbers. Then, they find numbers ten less than two other double-digit numbers. An explanation on the bottom half of this page walks scholars through the pattern in the tens place of any number with ten added to or subtracted from it. This would work best as a whole-class projection, since the answers are on the bottom of the page and can be covered.