## Who’s the oldest?

Katie’s birthday is on October 2.  Our school district’s policy for going to first grade is “6 years old by October 1”, and they are very strict about it.  Katie knows this fact, and fortunately, she is very happy about and proud of being the oldest in her class.  She often talks about how lucky she is in that regard.  A few days ago, I had the following conversation with her.

Katie: I wish everyone in my class knew that I am the oldest.
Me: How do you know that you’re the oldest?
K: Because I turned 6 first this year.
Me: How do you know that no one turned 6 before the school year started?
K: I just know, but some kids don’t believe that I’m the oldest.
Me: Well just tell them what you told me.
K: You see, my birthday is in October, and some kids’ birthdays are before October, so they think that they’re older.
Me: But what matters is not just when your birthday is, but also how old you’re turning.
K: I know, but if only December were not the last month of the year, but September was. Then October would be the first month and no one’s birthday would be before mine!

Today I found myself once again pondering over the source of the other kids’ confusion.  Then I gave Katie the following problem:

“Right now it is June and Anna and Becky are both 6.  Anna’s birthday is in January and Becky’s is in October.  Which girl is older?”

Katie immediately answered that Becky was older.  I then asked her to explain how she knew.

K: Because Becky is going to turn 7 in October and Anna is still going to be 6.
Me: So this is how you can explain to the other kids why you are older.
K: Oh, I already convinced them.

I decided not to ask how 🙂 .

I enjoy thinking about presenting mathematical concepts to young children in exciting and engaging ways.
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### 3 Responses to Who’s the oldest?

1. If she is still interested, then this is also an opportunity to talk about fractional ages.

In our 1st and 2nd grade classes, one of the warm-up exercises is talking about days of the week and months of the year, particularly what comes after/what comes before. There is never much stumbling for days of the week, but “before January” is consistently the hardest and “after December” second most difficult.

I wonder if they would like the question: what comes first, January or February? I guess most kids will agree on January. Ok, so January vs March, January vs April, etc? I wonder where consensus breaks down and they have to think carefully about what “before” means (if it has any meaning here).

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2. David says:

Hmm, is it too late to get Zoe to say, “I am three and three-eighths!”?

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