Missing Numbers to 50

Today I am going to try my best to trick you!! I am going to cover up a bunch of numbers and see if you can figure out what numbers are missing and then write those numbers in standard form.

Before we do that though, I want us to look closely at the 50 chart.

Guiding Questions: These questions help students focus on the structure of the 100 chart. They are noticing the structure and then using it to help them identify other missing numbers, which is an example of alignment to MP7, "Look for and make use of structure".

• What do you notice about how the chart is set up? What do you notice about how the numbers change/stay the same?

• Partner Talk: What other things do you notice about how the chart is set up?

I'll chart some of the ideas I hear in partners and refer to the class 100 chart. 

We noticed so many new things about how the hundreds chart is set up! This is going to help us as we work on reading and writing the numbers to 50. Remember that our thinking job is: How can I use what I know about a hundreds chart to figure out missing numbers?

I'll hide 1 number while students close eyes. "What number is missing? How do you know?"

I'll hide 3-4 more numbers and follows the same routine, always having students explain their reasoning for how they are sure. Students are working on MP3, Construct viable arguments and critique the reasoning of others, as they explain their thinking.

Missing Number Rules:

1. Partner 1 covers up 3 numbers with counters. Partner 2 can’t look!
2. Partner 2 opens eyes and guesses a number. Partner 1 shows them the number and says, “How do you know?” or “No, the answer was ___”.
3. Partner 2 guesses all the other numbers. Partner 1 has to ask “How do you know” or “No the answer was…”
4. Record the numbers that were hiding in standard form.
5. Switch! Keep playing until time is up!

I'll model a few rounds on the class hundreds chart, emphasizing the How do you know part. I'll reference the chart from earlier-“I see you know that all the numbers on this row start with a 2-we noticed that earlier on our chart”.

Guiding Questions:

• What did ___ do to figure out the missing number?
• Is there another way you can know for sure that is the number?
• How would we write that number?

Today’s thinking job was: How can I use what I know about the hundreds chart to help me figure out missing numbers?

I'll play one more round with students and closes out the day.