In today’s math talk, students will be exposed to a variety of questions that involve subtracting numbers to make the connection between subtracting from a teen number to make ten and the Down and Under Ten strategy. The consolidation of the math talk videos will allow students to see how the use of a ten frame or a number line can assist in explaining their thinking.
Prompts:
14 – 4
14 – 5
17 – 7
17 – 8
16 – 6
16 – 9
Show students the following visual math talk prompt and be prepared to pause the video where indicated:
The first part of this math talk draws on the relationship in teen numbers that has been discussed the whole unit. On Day two, the math talks subtracted 10 from a teen number, today’s math talks subtract the “ones” from the teen number to make a difference of 10.
A concrete number line is used in the consolidation of this prompt as a visual representation.
With this type of number line, the amount of spaces can be directly counted to confirm the 4 that have been removed.
Discuss with students that we can demonstrate this removal of 4 in just one jump on the number line without having to count back by ones because once we remove 4 from 14, there is 0 left in the ones/singles column.
The second part of this math talk, introduces students to the Down and Under Ten strategy. The idea of this “number string” is for students to use their knowledge of 14-4 in the first portion of the prompt and realize that one more is being removed.
Again the number talk has been used to as a visual tool to make the connection to the first part of the prompt.
We already know that 14-4 is 10, so now we are just subtracting one more.
Show students the following visual math talk prompt and be prepared to pause the video where indicated:
An open number line is used in the consolidation of this prompt. The freedom of the open number line allows students to create a jump that they feel has a value of 7. They do not need to get caught up in counting the amount of spaces.
In saying that, the open number line eliminates the opportunity for students to be able to directly count the spaces between 17 and 10.
This jump in sophistication may be difficult for some students. Consider having the concrete number line still available for students if needed.
Again, the numbers in this prompt are specifically chosen to continue from the first portion of this number string.
“If we already know 17-7, how can we solve 17-8?”
Show students the following visual math talk prompt and be prepared to pause the video where indicated:
The last number string still encourages students to use the information that they gathered to help them.
“If I know 16-6 is 10, how does that help me with 16-9?”
This is an example of using the Down and Under Ten strategy. If nine is decomposed into 6 then there is 3 more to subtract. Students may “just know” the answer is 7 because of their understanding with facts of 10.
Download the videos, images, and related media files to your computer to avoid streaming.
Download in Apple Keynote format to avoid streaming video and run the lesson smoothly.
Download in Microsoft PowerPoint format to avoid streaming video and run the lesson smoothly.
