The purpose of this activity is for students to learn Stage 2 of the Write Numbers center. Students choose to count forwards or backwards by starting at either of the numbers on a gameboard. Students take turns counting and writing the next one, two, or three numbers. The player who writes the last number on the gameboard wins. In this stage, students count by 10 starting at numbers other than 10.

Consider laminating gameboards or placing them in sheet protectors so they can be used multiple times.

• “¿Qué observan sobre cada número del tablero de juego?” // “What do you notice about each number on the gameboard?” (They all have the same amount of ones. The tens go up by 1 in each number.)

The purpose of this activity is for students to practice adding and subtracting 10 mentally from any two-digit number. The problems are organized into two sets. In the first set, students add and subtract 10 from the same number. Students may notice a pattern and generalize that when you add or subtract 10, the number of tens increases by one or decreases by one and that the ones place does not change (MP7). In the second set, students work with a range of numbers including adding or subtracting multiple tens to develop fluency.

If students find the values of the expressions by counting on or counting back by one, consider asking:

• “¿Cómo encontraste el número que hizo que esta ecuación fuera verdadera?” // “How did you find the number to make this equation true?”
• “¿Cómo puedes usar lo que sabes sobre decenas y unidades para encontrar el número que hace que la ecuación sea verdadera?” // “How can you use what you know about tens and ones to find the number that makes the equation true?”

• “¿Qué patrones observaron mientras sumaban o restaban 10?” // “What patterns did you notice as you added or subtracted 10?” (Only the tens place changes. In some of the equations I was adding 2 tens or 3 tens so it was like adding tens from before. I can skip count to add or subtract tens quickly.)