Getting Bigger and Smaller

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SWBAT extend their understanding of the base ten system using its properties to add, subtract and compare two and three digit numbers.

Big Idea

Students are extending their understanding of the base ten system by using its properties to add, subtract and compare two and three digit numbers.

Warm Up

10 minutes

I create a grid on the board and place a digit 1 in the hundreds place, digit 3 in the tens place and digit 2 in the ones place, leaving a blank in the middle for students to add < > =, and then place a digit 2 in the hundreds place, a digit 6 in the tens place and a digit 8 in the ones place.

1 hundred 3 tens 2 ones ______________  2 hundreds 6 tens 8 ones

(I have written the words so that students can think about what they know about base ten numbers (a Common Core requirement) and how the numbers are built. 

I read the descriptions aloud. I ask students to  write the numbers I am describing and add the greater than, less than or equal to sign in the middle. I remind them that the alligator likes to eat the larger number. 

I ask for a student to come up and write the two numbers and the sign on the board. I ask for a thumbs up from students who figured out the two numbers. 

(The child writes 132 < 268)

I write a second example on the board and repeat the process. 

3 hundreds 4 tens 1 one _____ 4 hundreds 3 tens 5 ones

If students are still struggling I may work through several more examples. 

I ask students to stretch and then come to the rug for the next part of the lesson.

Teaching the Lesson

30 minutes

Students have been hearing and using the terms digit, ones, tens and hundreds. We have not yet talked about expanded notation for numbers.

For most students, expanded notation was introduced in 1st grade where students learned that 11 is made up of 1 ten and 1 one, and twenty is made up of 2 tens. Today we will review this concept and expand it to include hundreds. 

I review expanded notation with students using base ten blocks, ask them to practice with me, and then they will have a chance to practice on their own. We will be able to add and subtract the blocks and compare our numbers as we practice.

I write the number 135 on the board. I ask a student which digit is in the ones place? I ask them to take that many ones out of the box. Next I ask which digit is in the ten's place and have a student take the right number of tens. I repeat this with the hundreds.

I write:

1 hundred, 3 tens and 5 ones in words next to the number and ask students if the two are equal? How do they know that the two numbers are equal? (I am looking for students to be able to identify that in the numeral 135 the one represents 1 hundred, the 3 represents 3 tens and the 5 represents 5 ones and that is the same as the words.) I help students to verbalize their understanding of how the words represent the digits in a number. 

I repeat the process with the number 269. 

Now I write:

1 hundred, 5 tens and 4 ones on the board. I ask a student to take the correct number of blocks. We check it together. I ask a student to come up and write the number on the board next to the words. 

I repeat this with the number 248.

Now I tell students that today they will be working in 3 groups, with numbers in the hundreds. Some will be building numbers and comparing them with the alligator (greater than less than mouths) and some will be adding numbers by building 2 numbers and then putting them together to create a new quantity. 

The students who can build numbers independently will work on adding two numbers. They will build both numbers reading the expanded notation form, building the numbers the words represent, and then combining the blocks to get an answer. This may allow them to trade 10 bundles of 10 for a 100 block. (MP1-Students are making sense of problems by using the models and then persevering in solving them.) 

The students who are still working on reading the expanded notation will build two numbers in the hundreds, and then compare them using the greater than/less than alligators.

Students will work for about 15 minutes of practice time.


15 minutes

Students return to the rug for a closing. This time I put two numbers on the board. I ask a student to show me which is greater using the <> symbol. 

Next I ask if anyone could come up and change the first number to 10 more. We discuss which digit should be changed to show a change of tens. I ask a student to do the same with the second number. Would the <> symbol change when I add 10 more to both numbers? Why or why not? Could it change if I added 10 more to just one number? When might that happen?

As we close I ask each student what 10 more than or 10 less than a number is. As they answer, they are free to line up for our move to specials. This is a quick check on their grasp of 10 more or 10 less.