The purpose of this activity is for students to use towers of 10 to physically add or subtract a ten from a multiple of 10. The structure of this activity encourages students to notice patterns in the count of tens and the numbers used to represent the count. Students connect adding and subtracting a ten to skip-counting forward or backward by ten and what they’ve learned about counting groups of tens in previous lessons (MP7, MP8).

• Display 7 towers of 10.
• “I have 7 tens, which is 70 cubes. How many will I have if I add one more ten? How can I represent it?”
• Invite selected students to share their representations.
• “How are these representations alike?” (They all show the same value.)
• “What did you notice each time you added a ten?” (The number was the next number you say when you count by ten. The number of tens was 1 more. One of the digits changed. It went up by 1.)
• “What did you notice each time you subtracted a ten?” (The number was the number you say when you count back by 10. The number of tens was 1 less. One of the digits changed. It was 1 less.)

The purpose of this activity is for students to learn Stage 4 of the Five in a Row center. Students choose a card that shows a multiple of 10 and decide to add or subtract 10 from the number on their card. They then cover the sum or difference on the gameboard with a counter. If students can’t make a number that is left on the gameboard, they pick another card. The game ends when a player gets 5 counters in a row or the board is filled.

The gameboard is provided as a blackline master. It will be used again in upcoming lessons. Consider copying it on cardstock or laminating it for future use.

• Invite 2-3 previously identified students to share how they added or subtracted 10.
• Display gameboard with some numbers covered by counters.
• Display a card.
• “Would you add or subtract 10 from this number? Why?” (I would add 10. Then I could cover _____. I would subtract 10. Then I could cover _____.)
• Repeat as time allows.

The purpose of this activity is for students to choose from activities that offer practice adding and subtracting. Students choose from any of the previously introduced stages of the listed centers. They are encouraged to choose the center that will be most helpful for them at this time.

• Five in a Row
• How Close?
• Number Puzzles

• “Han is playing Five in a Row—Add or Subtract 10. He picks a card with the number 60. What are the 2 numbers he could cover on his gameboard? How do you know?”