Review & Connect:
We have been looking at what addition sentence we can use to help us solve subtraction sentences. We have been seeing how those numbers are related. Today I am going to tell you a story that is your job to act out. In these stories, we are going to take away some, but we don’t know how many we started with.
Your thinking job is: How can I act out and write a matching number sentence for a problem when the first number is missing?
I'll start by telling this elaborate story! One of the Common Core shifts is that math should be contextualized in "real life" situations. To teach the challenging topic of start unknown, I want students to be grounded in what these kinds of problems could look like in "real life"!
Friends, last weekend I went to the circus. At the circus, I met the saddest little clown! This clown was walking around with only 4 balloons. I asked him, “Sad little clown! What is wrong?”
He said, “5 of my balloons flew away and now I only have these 4 left”
So I told him, “Sad little clown, I’ll get you some more balloons. But how many balloons did you have to start with?”
He looked at me so confused!! Today we are going to work on figuring out how many he started with.
I'll have a storyboard on my anchor chart. The chart will just have a simple box divided into 3 rectangles that are labeled: "First," "Next," and "Last". See completed Anchor Chart example!
To help us figure out how many balloons this poor little clown started with, we are going to have to figure out what really happened here.
Now I want to show what happened in pictures on my storyboard. Writers, readers, scientists, and mathematicians all use storyboards to help them organize their thinking in order of what happened-first, next, then, and last.
1. What happened first in this clown’s problem? (Push kids to say that at first he was at the circus and he had some balloons but we don’t know how many he started at first)
2. What happened next? (5 of his balloons flew away!) I’ll draw the little clown again but this time with a sad face because his 5 balloons are flying in the sky.
3. What happened last in the story? (He had 4 balloons left) I’ll draw the little clown with 4 balloons in his hand.
4. Now let’s see if we can represent his story with a number sentence. We can use a star for the missing part. How could I write the number sentence? Why did you put a star in the front of the sentence?
Partner talk: How could we figure out how many the little clown started with?
I'll quickly share out and model one student's strategy. I'll use the strategy that is the closest to acting it out. I'll pretend that 5 cubes are floating away and there are 4 left. Most kids will see you can just put all of the cubes back together!
Present Problem: The clown was playing at the circus with his balloons. Then 2 balloons flew away. He has 6 balloons left! How many balloons did the clown have at first?
Directions: I have a storyboard here for you. I want you to show what happened first in this story, next and last. Make sure you put a ? on the part of the story where we don’t know how many balloons.
Student Work Time: See Clown Storyboard_Student Share.docx for the student copy!
I’m going to make this super fun to get them invested in these problems. I’ll let them use crayons and spend 5-7 minutes on the storyboarding. If kids finish early, I’ll have them write a sentence for what happened at each part of the story.
I'll have students retell the story using their storyboards with a partner.
You can watch two little girls explain what happened first, next and last, as well as see examples of their work! The link is here!
After retelling the story using their storyboards, I’ll have students write the number sentence to match the story and use a heart to represent the unknown number.
Re-contextualize the number sentence: This is aligned to Mathematical Practice 2, which asks students to represent a story with symbols, but also to take symbols and be able to contextualize that back into a story.
Now I can look at your number sentence and tell this story! The clown had some balloons, but we don’t know how many. Then 2 of the clown’s balloons flew away. And he still has 6 in his hand. The heart will tell us how many balloons he had at first-or how many balloons he had in all.
Partner talk: How can we figure out how many balloons the clown had at first?
Students storyboard and solve problems similar to the problems we worked on together. See the attached Start Unknown Strategy Guide.docx for how students might solve. It gives some ideas for ways to push kids to a higher strategy level!
Group A: Intervention
Students storyboard only. I'll push them to just see the missing part and put a question mark there. All numbers under 10.
Group B: Right on Track
Students storyboard, write a number sentence to match and solve. Numbers to 10. Watch to see how kids solve-there strategy will probably be just to count all the balloons.
Group C: Extension
Students storyboard, write a number sentence to match, solve and writes words to explain their strategies. Numbers to 20. For today, because it is an introductory lesson, this will probably be a very small group.
I'll bring students back together and share one more story problem with them. We will quickly model how one person solved this problem. I always try to end the lesson with the strategy I want them to remember most, so I will choose a basic modeling strategy with cubes so kids start fresh with this strategy tomorrow!