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The purpose of this Number Talk is to elicit strategies students have for adding two numbers when one number is close to a ten. These understandings help students develop fluency in addition. Students may look for and make use of structure (MP7) in a number of ways. For example, they may add 1 to the first addend to make a full ten and subtract 1 from the second addend to find each sum. They also may notice how the addends compare to those in the previous expression and use the change to find the new sum.
In this string, students also may add the tens and the ones separately to find the sum. Adding by place value is the focus of upcoming work. This Number Talk also enables the teacher to learn the strategies students currently use for addition.
Find the value of each expression mentally.
The purpose of this activity is for students to find the areas of figures that are composed of rectangles but are not fully gridded with squares. Partially gridded figures help prepare students to find the areas of figures with only side length measurements. Students should be encouraged to find side lengths and multiply, rather than rely on counting, as the grids disappear. If students continue to draw in the squares, ask them if there is another way to find the area.
What do you notice? What do you wonder?
Find the area of each figure. Explain or show your reasoning.
The purpose of this activity is for students to find the area of a figure composed of rectangles, given only the side lengths of the rectangles. The context of paving a patio provides students a link to their experience with squares of various sizes and should help them imagine how the diagram of the patio could be covered with squares. Students decompose the patio into rectangles and can multiply to find the area of the patio, but they should make the connection that the number of pavers needed to cover the patio is the same as the area of the patio. When students connect the quantities in the story problem to an equation, they reason abstractly and quantitatively (MP2).
Noah wants to use square pavers to create a small patio in the community garden. A diagram of the patio is shown.
What is the area of the patio? Explain or show your reasoning.
“In this lesson, we found the areas of figures even if they were not fully gridded with squares. What did you need to think about when finding the area of a figure with just side length measurements?” (I can imagine it being filled with squares and counting them. I can break the shape into rectangles and multiply the side lengths and then add those areas together.)