Explore

In pairs, write a Separate (result unknown) word problem for 14-8=?. Make up a context that will be interesting to your students, has a starting value of 14, a change of 8, and the result is unknown.

The strategies that children use for addition/subtraction problems are listed below. Watch a video description of each strategy. You can read more about CGI Strategies here.

Direct Modeling

The child physically represents the objects described in the problem using manipulatives or drawings, and physically models the action of the problem. (Watch Separate (result unknown) Direct Modeling Video)

Counting

The child counts the numbers in the problem, but does not necessarily need the physical model. The child might use fingers to keep track of the counting, and might use skip counting as appropriate. (Watch Separate (result unknown) Counting Video)

Derived Fact

The child makes use of facts they already know to determine the solution to a problem they don’t know. They do not need to match the action of the problem. (Watch Separate (result unknown) Derived Fact Video)

Discussion

Discuss how children would solve the following problem using a direct modeling strategy, a counting-down strategy, and at least two different derived fact strategies.

Separate (result unknown) Word Problem

There were 12 birds on a tree branch. 5 of the birds fly away. How many birds are now on the branch?