The purpose of this activity is for students to interpret and solve a story problem by adding or subtracting within 100. Students solve an Add To, Start Unknown problem, one of the more difficult problem types from grade 1. Students begin the activity by looking at the problem displayed, rather than in their books. At the end of the Launch, students open their books and work on the problem.

Monitor for students who use methods that show adding or subtracting by place to share in the Synthesis. Students who choose to use connecting cubes or base-ten blocks or who draw a diagram to represent the situation are using tools strategically (MP5). During the Synthesis, invite all students to explain why these methods work using their understanding of place value.

This activity uses MLR6 Three Reads. Advances: reading, listening, representing. Some students may benefit from continued use of MLR6 to support reading comprehension in Activity 2.

• Invite previously identified students to share.
• Record student methods using equations. 
• “How are these methods the same?” (They both show tens and ones. They both thought of keeping the tens with the tens and ones with the ones.)

The purpose of this activity is to solve different story problems by adding or subtracting within 100 without composing or decomposing a ten. Each problem elicits the relationship between addition and subtraction and can be solved with either operation. Students are encouraged to describe methods based on place value and should have access to base-ten blocks. In the Synthesis, students compare representations and make connections between concrete representations and drawings. 

Invite students to use the Three Reads routine to support reading comprehension. Some students may also benefit from reading the story problems with their partner before working independently.

• Invite previously identified students to share. Consider selecting a student who used base-ten blocks first, followed by a student who used a base-ten drawing. 
• If no students use a base-ten drawing, draw one to record the way a student uses their blocks to represent and solve the problem.
• “How are these representations the same?” (Both started by representing 88 birds. _____ moved away 3 tens and 4 ones, and _____ crossed out 3 tens and 4 ones.)
• 1 minute: quiet think time
• Share responses.