category 1 encourages removing the subtrahend (part) in parts that are the same as the digit in the...

Category 1

Encourages removing the subtrahend (part) in parts that are the same as the digit in the minuend (whole). Please

see page 150 in Number Talks for an explanation of using this strategy efficiently.

Example: 21 – 9 = Decompose 9 to 1 + 8 so 21 – 1 = 20 and 20 – 8 = 12

12 – 212 – 515 – 515 – 6

13 – 313 – 513 – 613 – 8

20 – 520 – 620 – 720 – 8

21 – 121 – 623 – 323 – 6

24 – 424 – 524 – 824 – 9

22 – 222 – 422 – 522 – 8

35 – 535 – 635 – 835 – 9

41 – 141 – 441 – 641 – 8

52 – 252 – 753 – 353 – 8

Category 2

Encourages removal in place value chunks without regrouping.

20 – 1020 – 1630 – 1030 – 12

26 – 1026 – 1328 – 1028 – 15

35 – 1035 – 1335 – 2035 – 24

47 – 1047 – 1647 – 2047 – 24

39 – 1039 – 1339 – 2039 – 22

56 – 1056 – 1256 – 3056 – 35

78 – 2078 – 2378 – 5078 – 54

69 – 3069 – 3569 – 5069 – 52

87 – 4087 – 4487 – 5087 – 53

Category 3

Encourages removal in place value chunks and decomposing a single-digit number to remove it in

parts

25 – 1025 – 1635 – 1035 – 16

32 – 1032 – 1332 – 2032 – 13

37 – 2037 – 2842 – 2042 – 23

23 – 1023 – 1536 – 1036 – 19

41 – 2041 – 2345 – 2045 – 28

52 – 2052 – 2538 – 1038 – 19

54 – 1054 – 1852 – 3052 – 34

58 – 2058 – 2951 – 3051 – 35

63 – 4063 – 4466 – 3066 – 38