work on problems that involved regrouping. She chose a word problem because
she wanted them to be able to make sense of a subtraction situation and connect
their strategies to an actual situation. This also gave them a context in which to
ground their strategies.
In the video, three students share their strategies for solving the problem.
Ana asks them questions about their strategies to make their thinking clearer for
herself and the other students and to help one student recognize and correct a
mistake she has made. She uses the information she learns about their under-
standing to plan future lessons.
When students are asked to develop and use strategies that make sense to
them, the strategies they use to solve subtraction problems usually fall into four
basic categories: subtracting in parts, adding up or subtracting back, changing the
numbers to numbers that are easier to subtract, or subtracting by place (Russell
et al. 2008h). (You might solve the problem yourself and take note of which cat-
egory your strategy fits in.) Here are examples of strategies students might use to
solve the problem 62 – 48:
How Many Children Got off the Bus?Subtracting in Parts Adding Up or Subtracting Back
62 48
62 40 22
22 2 20
20 6 14 (the 48 can be broken
apart in a variety of ways)
62 48
48 2 50
50 12 62
2 12 14
or
62 2 60
60 10 50
50 2 48
2 10 2 14Changing the Numbers Subtracting by Place
62 48
62 50 12
12 2 (took away 2 too
many, needed to add back on 2)
or
(add 2 to both numbers)
62 48 64 – 50
64 50 14
(^5) 6/ (^12)
- 48
14
or
60 – 40 20
2 – 8 –6
20 – 6 14