4th grade: Can This Be True?

In this Number Talk, Elysha Passeggi engages her 4th grade students in a discussion about whether or not the sum of two two-digit numbers can be 238. Students share their responses, defend their thinking, and formulate declarative statements about why the problem is definitively false.

 JW Player goes here Elysha Passeggi introduces the day’s number talk, reminding the students of a previous number talk in which they were to solve without calculation, instead looking at relationships of the numbers or considering “fact families.” For the first problem of the day, she asks the students to identify “whether the equation is true or false, and how do you know.” Her first problem, 5 + 7 = 12, reaches rapid consensus among the students. The second, 21 + 39 = 50, trips up some students. The students share different approaches to considering the problem. One notes, “You can’t go through it really fast, because then you miss all the calculations.” “Let’s try a challenge problem,” Passeggi says to her students. She gives them a problem where some number is missing; “What number do you need to put in this box to make the number sentence true?” for 8 + 4 = ____ + 5 . The next problem requires the same approach: 12 + 7 = 8 + ___. Passeggi asks “Is anybody noticing anything?” to ask the students to identify the pattern in the two problems. One student shares that “automatically, I know that the one in the box is going to be one less.” She proposes a third problem to “test if that way will work.” After each student shares their way, Passeggi asks the group to raise their hands if they “saw it that way” as well. The students refer to the methods of solving by attaching them to the student’s names, i.e. “I did what Quinn did.”