My son, “Daddy, what’s 192 plus 192?”

Me, “What’s 200 plus 200?”

My son, “400.”

Me, “What’s 192 plus 192 then?”

My son, “I don’t know.”

Me, “Try breaking it down like this. 100 plus 100 plus 90 plus 90 plus 2 plus 2. Does that help?”

My son, “Hrmm. Okay, it’s 284. No, I mean 384. Do you want to know why I want to know?”

Me, “Absolutely. Why do you want to know what 192 plus 192 is?”

My son, “I started with 1 plus 1, and now I’m at 8192, and I want to know what 8192 plus 8192 is.”

Me, “Do you mean you added 1 plus 1 to get 2, and then 2 plus 2 to get 4, and so on?”

My son, “Yes.”

What makes this exchange especially interesting to me is that I remember attempting to do exactly the same calculations my son is doing, at about the same age.

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Age?

He’s 7.

I remember having a similar conversation with a group of second grade students last school year. The question was 195 + 191. I asked them to think about doubling (200 + 200) and then subtract from there. Interestingly enough, all decided to add the numbers based on place value. Some even asked for whiteboards to complete the problem. Students were challenged by the tens place in this problem. Eventually all students were on the right track and found a solution, but it made me think of how the strategy that they chose compared to doubling and subtracting.