In a previous lesson, students used a subtraction algorithm in which single digits were used to record the result of subtraction in any place-value position, and one or two digits were used to record any decomposition. They decomposed, as necessary, before beginning to subtract. In this lesson, students make sense of and use an algorithm in which subtraction begins with the ones, decomposing units as needed as they work from right to left. Students also consider a case in which it is necessary to decompose a hundred and a ten in order to get more ones because there is a zero in the tens place.

How did your students use their prior understanding of subtracting with an algorithm to solve problems in which they have to decompose place-value units across zeros?