At dinner tonight, I asked DS (6.5) what 7x10 was. He said 70 right away.

Then I asked him a question I knew was hard for him... What is 7x7?

In his head (no paper to write on) he figured (and talked) out this formula:

10x7=70

10-7=3

2x7=14+7=21
so...
70-21=49

7x7=49

I didn't know he could do that.
He's memorized a lot of the times table, but some like 7x7 always seem to stump him.