# Counting with Tens and Hundreds

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## Objective

SWBAT add or subtract 10 from any 2 digit number and use a model to add or subtract 100 from any 3 digit number

#### Big Idea

Being able to add and subtract with 10 and 100 is a Common Core skill expected of second grade students.

## Warm Up

10 minutes

To support the Common Core standard of being able to add and subtract 10 from a number mentally, we begin by practicing partners of ten mental math. I call out a partner of ten fact and students respond by holding up the number of fingers to make 10. I call out 6, they hold up 4. I call out 9, they hold up 1.

Next, to recall prior learning of equal number sentences, I put the number sentence 16 + 4 = ___ + 8 on the board. Students find the missing number. I ask students to identify the partners of ten that they see in the equations.

I repeat this with another sentence. 12 + ____ = 9 + 11. We comment on the partner of ten found within the sentence.

I tell students that today we will begin on the rug. I ask them to count back from 20 as they walk to the rug.

## Teaching the Lesson

15 minutes

To meet the diverse entrance points of the learners in my classroom, I create several different IN/OUT tables for students to work on independently. I want all students to be challenged, but not overwhelmed.

One group will work with adding and subtracting with 5s and 10s in the IN/OUT boxes. Another group will extend their understanding by adding and subtracting with money (dimes and dollars) in their IN/OUT boxes.

Each group will also have a chance to work with a cardboard IN/OUT machine and to explore how the numbers are changing and to see if they can apply that change to different numbers.

The independent practice will allow students to explore the adding and subtracting of 10 and 100 from a number. I want students to begin to internalize this process so that it becomes automatic and rather than having to count, they can realize that by using the idea of place value, they can change just the tens or hundreds place up or down.

## Independent Practice

20 minutes

To meet the diverse entrance points of the learners in my classroom, I create several different IN/OUT tables for students to work on independently. I want all students to be challenged, but not overwhelmed.

One group will work with adding and subtracting with 5s and 10s in the IN/OUT boxes. Another group will extend their understanding by adding and subtracting with money (dimes and dollars) in their IN/OUT boxes.

Each group will also have a chance to work with a cardboard IN/OUT machine and to explore how the numbers are changing and to see if they can apply that change to different numbers.

The independent practice will allow students to explore the adding and subtracting of 10 and 100 from a number. I want students to begin to internalize this process so that it becomes automatic and rather than having to count, they can realize that by using the idea of place value, they can change just the tens or hundreds place up or down.