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Answer to Problem 8: Answers may vary. Examples:

25 – 8 = 17 or 25 – 17 = 8

25 – 9 = 16 or 25 – 16 = 9

17 – 8 = 9 or 17 – 9 = 8

DEFINITION:

decomposing and composing numbers—flexibly using or knowing numbers through creating and breaking numbers apart to form equivalent representations. For example, 36 can be thought of as 32 + 4, 20 + 16, 40 – 4, 12 ´ 3, etc.[1]

TEACHER NOTES:

Students who have developed number sense are able to think about numbers flexibly. They recognize that in order to work with numbers mentally, they can split numbers apart to make combinations that they already know.

This flexibility builds an understanding of number as a specific quantity as well as a relationship between and among numbers, which allows students to compute with numbers mentally.

Being able to break a number into a multiple of 10 or 25 allows students more strategies to think about the number.