The purpose of this activity is for students to use place value reasoning and properties of operations to determine whether they would compose a ten when adding a two-digit and a one-digit number.

Students write equations to show how they solved, such as:

It isn't important that students write their equations in this way, but it is important that they can relate each part of the equation to how they found the sum.

Students may write . Since this equation is not true, it is important to remind students that the equal sign means “la misma cantidad que” // “the same amount as” and that it is necessary to use two separate equations.

• Invite previously identified students to share.
• “Pensemos un poco más sobre cómo sabemos si vamos a formar una nueva decena o no” // “Let’s think some more about how we know whether or not we will make a new ten.”

The purpose of this activity is for students to deepen their understanding of place value and properties of operations when adding one-digit numbers and two-digit numbers. Students find an unknown addend that fits a specific rule for each expression. Some expressions have more than one number that fits the rule. As students complete each expression, they look for and make use of structure (MP7) as they think about whether or not the ones in the two numbers will combine to make a new 10.

During the Activity Synthesis, students look at different one-digit numbers that would make or not make a new ten when added to 16. In the Lesson Synthesis, students share their answers to the last problem in the task which encourages them to make generalizations (MP8).

• Display

  

• “¿Qué números de 2 dígitos puede ella sumar que formen una nueva decena?” // “What 2-digit numbers can she add that will make a new ten?” (12, 35, 49)
• “¿Qué números de 2 dígitos puede sumar que no formen una nueva decena?” // “What 2-digit numbers can she add that will not make a new ten?” (11, 30, 41)
• “¿Qué observan sobre cada lista de números?” // “What do you notice about each list of numbers?” (If she doesn't make a new ten, the number can only have 0 or 1 in the ones place, but it can have any number in the tens place. If she does make a new ten, the number can have 2, 3, 4, 5, 6, 7, 8, or 9 in the ones place.)