A Second-Grade Boy Is Asked to Subtract 64 - 55

Short Answer

A second-grade boy is asked to subtract 64 - 55, written vertically. The child thinks about the problem and then writes 9. He explains his thinking by saying, "6 take away 5 is 1. I mean, 60 take away 50 is 10. 5 take away 4 is 1, and 10 take away 1 is 9." Is he correct? Use his thinking to find 243 - 124.