Count on using the number path to find an unknown part.

In this lesson, students continue understanding subtraction as an "unknown addend" problem, and begin relating counting on to subtraction. They use a number path to solve related addition and subtraction problems by finding one part, counting on to the total, and determining the number of counts it took to get to that total from the part. For example, they relate the number sentences 8 - 5 = ___ and 5 + ___ = 8. Then they start at 5 on the number path, count on to 8 ("Five...six, seven, eight!"), and note that it took 3 counts to get there.