Teacher: Look at all the problems with zero in them. Can
someone read them to me? I will write them on the board. Look
for a pattern that will help solve these problems.
Michael: 1 − 0 = 1, 2 − 0 = 2, ... 10 − 0 = 10
Teacher: Michael, where did you find these problems on
the chart?
Michael: I found one in each group.
Lee Yah: I see a pattern. All the answers are the same
as the first number in the problem.
Teacher: Well said, Lee Yah. Why do you think that
works? What does it mean to subtract zero? What are you taking
away each time?
Lee Yah: You take away zero which is nothing. So if you
take away nothing, then the other number stays the same.
Teacher: Which problems did you think were easiest? How
did you solve them?
Jacob: The ones with zero were easiest because you could
just say the other number.
Keenya: I could do the ones that took away 1 or 2 the
fastest.
Teacher: How did you solve them? Pick a problem like
that and show me how you solved it.
Jackie: For 8 – 2, I started with 8 and counted back two
on my fingers, 7, 6. It's 6.
Teacher: Which ones do you think were hardest?
Tanya: I got stuck on 9 – 6, so I just used my cubes. I
built a train of 9 and took away 6 and got 3.
Teacher: Is Tanya right? Did someone solve that one a
different way? What answer did you get?
Nila: We had that problem with the bags, so I started at
6 counted up 7, 8, 9. That's means the answer is 3.
Teacher: So, you agree with Tanya. You two did it
different ways but got the same answer. What is another hard
problem?
Jessie: 10 – 6 was hard, but I thought to use my number
line and it helped.
Teacher: Come show us what you did on the class number
line. [Jessie points to 10 on the class number line and shows
6 hops back to 4.]
Jessie: See it is 4.
Teacher: Did anyone use a ten frame to solve this
problem? [After a pause] Nicholas, what did you and Roberto
decide to do?
Nicholas: We knew to start with ten, so we just imagined
that the ten frame was full of dots. Then we pretended to take
6 off. [Nicholas puts a finger in the last box on the ten
frame and counts backwards across the bottom row and then
covers the last box in the top row with his finger.] So we
know that there are 4 boxes left.
Teacher: Roberto, what is a number sentence for that
problem?
Roberto: 10 – 6 = 4.
Irma: When we looked at the ten frame, we remembered how
we made addition and subtraction sentences.
Teacher: How did that help you solve the problem?
Irma: We knew that 6 + 4 = 10, so 10 – 6 = 4.
Teacher: So Irma used addition to help her solve a
subtraction problem. Talk with your partner and think how you
can use addition to solve 9 − 5. You might want to look at the
addition chart. [After a pause] Michael, how did you and Ming
use addition to solve the problem?
Michael: We were stuck, but we looked on the chart at
the group of nines. We saw the card that said, "5 + 4 = 9," so
9 – 5 must be 4.
Teacher: That is very good thinking. You have all used
some good strategies. You used patterns, tools, counting, and
addition to help solve subtraction problems.
