Solve add to with change unknown math stories as a context for counting on by drawing, writing equations, and making statements of the solution.

This lesson introduces the "add to with change unknown" problem type, where the action, which represents the change, is unknown (for example, "Ben has 5 pencils. He got some more from his mother. Now, he has 9 pencils. How many pencils did Ben get from his mother?"). They use counters or drawing pictures to add more to a starting quantity and learn to count on to determine the unknown part (the number it takes to reach the total).