Adding and subtracting ten is an easy and fun way to understand how numbers change. When we add ten, the number becomes greater by ten. For example, 5 + 10 = 15, 8 + 10 = 18, 12 + 10 = 22, 20 + 10 = 30, 25 + 10 = 35, 30 + 10 = 40, 40 + 10 = 50, 50 + 10 = 60, 60 + 10 = 70, and 70 + 10 = 80. Each time we add ten, the number increases by one in the tens place. When we subtract ten, the number becomes smaller by ten. For instance, 80 – 10 = 70, 70 – 10 = 60, 60 – 10 = 50, 50 – 10 = 4