Hi, my name is Diane Sipple. I teach third grade at George's Creek Elementary.
Today, I'm going to model subtraction within 1,000 using an open number line.
Today's problem is there are 372 students going to the zoo on two buses.
143 students will be on the first bus. How many students will be on the second bus?
This problem is asking me to find the difference between the two numbers
so I'm going to use subtraction to solve it.
I'm going to open the learning apps program to demonstrate
solving this problem on the open number line.
First, I'm going to write my problem
372
minus 143.
I'm going to start by plotting 372 on the right side of my number line.
Now, I'm going to show taking away
143. I'm counting back 100,
10, 20, 30, 40,
1, 2, and .3
Starting with 372 when I subtract 100
the difference is 272.
When I subtract my first 10 from 272
my difference is 262.
When I subtract my second 10
the difference is 252.
When I subtract my third 10
the difference is 242. And when I subtract my last 10
the difference is 232.
I'm going to record that to show that I took away all 40 of my tens.
Now, I'm going to subtract by ones.
232 minus 1 is
231
minus 1 is 230 and
minus one more for my final one is
229.
So when I subtract 372 minus 143 it equals
229.
