The purpose of this activity is for students to find differences using methods they choose. As students work, they may feel more comfortable with one method than another. The numbers were chosen to encourage different methods (counting on and taking away), so students can consider the numbers in a specific expression as they find the difference. During the Activity Synthesis, students share which method they used for a specific problem and why they chose it (MP3).

• Invite previously identified students to share.
• “Podemos escoger qué método usar para encontrar valores desconocidos en distintas ecuaciones dependiendo de los números que aparecen. Si hay que quitar mucho, podríamos, más bien, contar hacia adelante. Pero si hay que quitar poco, podríamos simplemente usar el método de quitar. Ambos métodos sirven, pero podemos pensar en cuál es mejor para cada ecuación” // “We can choose to use different methods to find unknown values in different equations depending on the numbers. If we need to take away a lot, we might choose to count on instead. If we only need to take away a few, we might choose to take away. Both methods will work, but we can think about which method is best for each equation.”

The purpose of this activity is for students to solve different types of story problems involving teen numbers. Each story problem can be solved using either addition or subtraction. Students may use either operation for the second and third problems and any method that makes sense to them. If they write equations to match the stories, they should be able to explain how the story and equation match (MP2).

• Display Kiran’s story problem.
• Invite previous identified students to share their methods and equations.
• “¿De qué manera sus ecuaciones corresponden a su trabajo? ¿En qué parte de la ecuación vemos la respuesta a la pregunta?” // “How do their equations match their work? Where do we see the answer to the question in their equation?”