# 3. Decomposing the numbers 11-19 by grouping ten and 1-9 ones (FP)

teaches Common Core State Standards CCSS.Math.Content.K.NBT.A.1 http://corestandards.org/Math/Content/K/NBT/A/1
teaches Common Core State Standards CCSS.Math.Practice.MP7 http://corestandards.org/Math/Practice/MP7

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Lesson objective: Decompose numbers from 11 to 19 into ten ones and some further ones.

This lesson helps to build fluency with decomposing the numbers 11 to 19. Ten frames, counters and numeral cards is used here because it supports students' understanding that teen numbers contain 10 ones and shows the extra ones while giving them the opportunity to match the collection to a numeral card that identifies how many. This work develops students' understanding that the numbers 11-19 are composed of ten ones and one, two, three, four, five, six, seven, eight, or nine ones.

Students engage in Mathematical Practice 7 Students look for and make use of structure as they work to decompose the numbers 11-19 to discover that each contains 10 ones by placing them on the ten frame and some extra ones below the frame.

Key vocabulary:

• compose
• decompose
• "teen" numbers

Special materials needed for each pair of students:

• cups with 11 to 19 counters
• labels/numeral cards (11, 12, 13, 14, 15, 16, 17, 18, 19)
• ten frames
• recording sheet
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