[Rescued from my old blog.]
My youngest daughter wanted to do Singapore math today. Miquon Red is her main math text this quarter, but we add a bit of Singapore Primary Math 1B whenever she’s in the mood. We turned to the lesson on subtracting with numbers in the 30-somethings. The first problem was pretty easy for her:
30 – 7 = []
I reminded her that she already knows 10 – 7. She agreed, “10 take away 7 is 3.” Then her eyes lit up. “So it’s 23! Because there are two tens left.”
Denise Gaskins' Let's Play Math 