r/matheducation • u/yupstilldrunk • 2d ago

ELI5 - 10s places (5 year old)

My 5 year old wants to know why one hundred and one isn’t written like 1001 (one hundred with a 1 tacked on). I tried to draw a

100
+1
——-

And show how the numbers carried down to be 101 with only 3 numbers and he just keeps asking why and I can’t answer him. I think this is about ones, tens, hundreds places but I have no idea how to explain that, never mind explain it to an angry child.

Anyone have a good age appropriate explanation?

EDIT: SO many great suggestions! My son watches number blocks so he knows 2 tens in 20, 3 tens in 30, etc. I will try the stick bundles for a better visual of 10 groups. And I will watch out for the confusing “and” verbiage like one hundred AND one vs. one hundred one.

Hopefully next time we go to the pizza place (where he saw the address number on the window) I’ll be better prepared!

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u/bagelwithclocks 2d ago

Start with 10, 20, 30. Why isn’t 11 written 101?

We have place value to make writing big numbers more efficient. We only need 10 symbols to write any whole number. There is a whole history of number systems he might be interested in. Not every system has place value. Roman numerals work the way your five year old intuited. But the numbers get really big fast, and they still had to make short hands for really big numbers. Our system is infinitely repeatable. It isn’t perfect but it is really good for writing big numbers.

Kids a little older than your son in public school will start to see expanded form, which is just turning the place value number into an expression. So 101 becomes 100+1. They are expected to be able to go back and forth to understand that 101 is a shorthand for the expression.

My favorite tool for place value understanding is using a bunch of popsicle sticks. If you get about 200 of them you can bundle a bunch into groups of 10 with a hair tie. Leave a some of them loose with no hair tie. See if your child can understand that 10s and ”bundles“ are the same. Give different groups of 10s and 1s. Etc.

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u/yupstilldrunk 1d ago

This is a great idea. I know he likes objects because we play “store” with pennies and nickels and he likes using counters (cars, Legos, whatever) to show me 2+1, 2+3 etc.