Strategize to solve take from with change unknown problems.

In this lesson, students use various strategies to solve "take from with change unknown" problems. (For example, "There were 11 birds in a tree when I first looked at it. I looked away. When I looked back, there were 5 birds. How many birds flew away?") They begin to recognize that although stories may be "take from with change unknown" problems, they can apply many strategies such as counting on, counting back, taking from ten, or getting to ten to accurately solve this challenging problem type.