TMWYK What if you

Here's an exchange I had with my almost-7-year-old where I use "What If" to stretch his thinking a bit further:

Me: Hey, why did you choose 7-2=5 for this stretch your thinking question? Is it because you just did that one on #5?

Him: "No! It's because 7 is my favorite number. And then the other one had to be 2 to make 5."

Me: "Oh, I see. Well I have a challenge for you then. I say you can use your favorite number 7, but you have to put it in the other box. What would go in the first box then? But that's probably too hard for you, right?"

...

Him: Counts on his figures, and a moment later says, "it's 14." Then added, "Wait, that's not right.... Is it?"

Me: "You tell me. Let's finish the rest of the homework (other side). But when you know you have the right answer to this one, (_)-7=5, you can tell me. But I don't want guesses. You tell me what it is when you know it's right. And then you can tell me how you were so sure. I can't wait to find out how you think about this one!"

Him (later): In no uncertain terms, "It's 12, and I can prove it!"

Him: Holds up 12 fingers by flashing 5 & 5 and then 2. "That's 12, he said, and to take away 7, you can take away the 2 first, and then 5 more. What's left is the other 5. So 12-7=5, Ha!!"

Me: "That's awesome Adam, I totally get that argument. Nice job!"