Lesson 21

• Display the number 20.
• “What do you know about 20?”
• 1 minute: quiet think time

• Record responses.

• “What connections do you see between different answers?”
• Pick two addition expressions that use different addends and ask, “How are these two expressions related?”

The purpose of this lesson is for students to learn stage 1 of the center, How Close? Students pick a given number of digit cards and then choose a subset of those to make an expression that yields a number as close as possible to 20.

• Groups of 2
• Give each group a set of number cards, two recording sheets, and access to double 10-frames and connecting cubes or two-color counters.
• “We are going to learn a game called How Close? Add to 20. Let's play the first round together.”
• “First we take out any card that has the number 10. We will not use those cards for the game.”
• Display 5 cards.
• “I can choose two or three of these cards to add to get as close to 20 as I can. What cards should I choose?”
• 1 minute: quiet think time
• 2 minutes: partner discussion
• Share responses.
• “I write an equation with the numbers I chose and the sum of the numbers.”
• Demonstrate writing the equation on the recording sheet.
• “The person who gets a sum closer to 20 gets a point for the round. Then you each get more cards so you always have five cards to choose from. Play again. The person who gets more points wins.”

• 10 minutes: partner work time

• Invite students to share their methods for making a sum close to 20. 

The purpose of this activity is for students to learn stage 3 of the Five in a Row center. Students choose to add 7, 8, or 9 to the number on their card and then place their counter on the sum on the gameboard. The first partner to have five counters in a row wins.

• Groups of 2
• “We are going to learn a new way to play Five in a Row.”
• Display the gameboard and pick a number card.
• “I can decide to add 7, 8, or 9 to the number on this card. What should I add?”
• 30 seconds: quiet think time
• 1 minute: partner discussion
• Share responses.
• Choose 7, 8, or 9 to add to the number and find the sum.
• “Now I put a counter on the sum on the gameboard. Then it is my partner's turn. Continue playing until someone gets five counters in a row.”

• 10 minutes: partner work time

• “What method did you see your partner use to decide whether to add 7, 8, or 9?”