# A Complex Argument

**What To Look For In This Video**

- This 3rd Grader has had lots of experience with word problems. She already understands what it means to "take away" 25 from 63.
- And she already understands that she can think of 2-digit numbers in terms of tens and ones. In particular, she thinks of 25 as 2 tens and 5 ones and 63 as 6 tens and 3 ones.
- She took the 2 tens of the subtrahend from the 6 of the minuend - without saying that that is what she was doing.
- She then broke up an additional ten of the minuend. She recorded "30" to represent the 3 tens that she had left.
- In order to now take 5 ones, she took the 3 ones of the minuend and then 2 additional ones from the ten that she had broken up.
- That left her with 8 ones - which she recorded.
- She is able to explain her work - in effect
**proving**that her answer is correct.