## Grade 1 Mathematics Module 1, Topic H

With a smooth transition from Topic G, Topic H provides students with rich experiences connecting subtraction to their solid foundation of addition (1.OA.4), using various word problem types (1.OA.1). Lesson 28 begins with students solving action-based take from with result unknown problems, as they begin with a set of objects, then take some away, and finally end with a smaller set of objects. Students then work with simple math drawings and equations to represent these take from with result unknown stories, and connect the act of crossing off to the symbol for subtraction. Then lesson 29 allows students to solve the relationship-based take apart with result unknown problems, which are both connected to take from with result unknown problems and are the counterpart to the familiar put together with addend unknown problems from earlier topics. In both Lessons 28 and 29, students make varied statements to explain the remaining amount, e.g., “There were 4 bears left,” “4 bears stayed in the forest,” “Then there were 4 bears altogether.” This permits students to think and speak flexibly about the unknown, rather than associating specific key words with a particular operation. For example, altogether does not always necessitate addition. Lesson 30 furthers the connection between addition and subtraction as teachers have students discuss ways to attack add to with change unknown word problems, as they use simple math drawings and equations to represent the problem and solution. With the introduction of a whole new problem type in Lesson 31, students use drawings to solve take from with change unknown problems such as, “Ben had 7 pencils. He gave away some. Now he has 5. How many pencils did he give away?” The topic ends with another new relationship problem—put together/take apart with addend unknown. Throughout Topic G, students discuss and apply their understanding of addition as it relates to subtraction and vice versa. A Teaching Sequence Towards Mastery of Subtraction Word Problems