In Lesson 4, students are going to memorize subtraction by one, two or three. First, study the facts in Part 1. Use your pencil to point to each problem as you study, but do not write anything down yet (just say the answers aloud or think about the answers in your head). Next, when you are comfortable and know all the answers in Part 1, quiz yourself. See if you can write all the answers in the column in less than 30 seconds. After students complete part one, they repeat the procedure for parts two, three and four. In part two, students subtract two. In part three, students subtract three. And in part four, students subtract one, two or three.