N1C2TNp4

Answer to problem 4:

TEACHER NOTES:

Students should have numerous opportunities to do quick images to be able to compose and decompose numbers. These experiences should include numbers between 10 and 99. Students who are accustomed to decomposing and composing numbers will use these strategies naturally as they make sense of addition and computation of larger numbers. For instance, a student may mentally combine 37 and 28 using several of the following strategies:

• combining the 30 and 20 to get 50 then combining the 7 and 8 to get 15 and finally combining the 50 and 15 to get 65,
• combining 40 and 28 (40 being 3 more than 37) to get 68 then subtracting the extra three to get 65,
• combining 40 and 25 (taking 3 from the 28 to combine with the 37) to get 65.[1]

DEFINITIONS:

compose or decompose numbers—flexibly using or knowing numbers through creating and breaking numbers apart to form equivalent representations. For example, knowing that there is a “3” and a “1” in 4 allows a student to think about 27 + 14 as being 20 + 10 + 7 + 3 + 1 or 30 + 10 + 1.[2]

landmark numbers—numbers that provide a foundation for extending number sense concepts. For example, at the second-grade level generally include sums of tens and getting to the next ten or counting by fives.[3]