Singapore Math: Grade 3a, Unit 2 (Part 9)

Sal uses numeric expansion to show the process of subtracting four-digit numbers. For example, he expands the number 6004 and writes it as 6000+0+0+4 and 2678 as 2000+600+70+8. When he regroups, viewers can see the actual number exchange when borrowing from a neighboring number. He follows up with several practice problems.