Adding and Subtracting Within 10

Objectives

Students will develop strategies to add and subtract 10 from off-decade two-digit numbers. They will:

use skip-counting patterns forward and backward by 10 to 100 off the decade and backwards by 10 on the decade.
alternate between tens and ones when adding and subtracting from decade and off-decade numbers.

Essential Questions

How are relationships represented mathematically?

How can mathematics support effective communication?

How can recognizing repetition or regularity assist in solving problems more efficiently?

How is mathematics used to quantify, compare, represent, and model numbers?

What does it mean to estimate or analyze numerical quantities?

What makes a tool and/or strategy appropriate for a given task?

What makes a tool/strategy appropriate for a given task?
How are relationships represented mathematically?

Vocabulary

Sum: The result of addition.

Duration

60 minutes

Prerequisite Skills

Prerequisite Skills haven't been entered into the lesson plan.

Materials

base-ten blocks
numeral cards 11–99 (If you don’t have cards, you can cut apart a hundreds chart)
number cube with –10 and +10 (A standard six-sided number cube can also be used. Cover the even numbers with a green sticker to indicate +10, and the odd numbers with a red sticker to indicate -10.)
Lesson 3 Exit Ticket (M-1-2-3_Lesson 3 Exit Ticket and KEY.doc)

Related Unit and Lesson Plans

Related Materials & Resources

The possible inclusion of commercial websites below is not an implied endorsement of their products, which are not free, and are not required for this lesson plan.

http://illuminations.nctm.org/ActivityDetail.aspx?ID=75

Formative Assessment

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- Observations during small-group work, student interaction, and whole-class discussion will serve to assess student progress.
- The Lesson 3 Exit Ticket (M-1-2-3_Lesson 3 Exit Ticket and KEY.doc) will serve as a review of the strategies students were exposed to in Lesson 3 and can be used as a formative assessment.

Suggested Instructional Supports

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Scaffolding, Active Engagement, Modeling, Explicit Instruction

W:	Make base-ten blocks available to the students as they begin to add and subtract 10.
H:	Have students identify what happens when you add and remove 10 from a given set of base-ten blocks.
E:	Students will use their understanding to play a game in which they add/subtract 10 from a decade number based on the roll of a number cube.
R:	Allow students to work as partners during whole-group discussion and as a part of the number-cube rolling activity.
E:	Monitor student discussions as an informal assessment. Have partners discuss the various strategies they used to attain the goal number.
T:	Give students a similar activity, daily or frequently, to mentally solve +10 and –10 problems. If students need more practice, they can work in small groups, using base-ten blocks and discuss which strategy can be used to achieve their goal. If students are ready, have them begin subtracting 10 from off-decade numbers.
O:	This lesson is designed for students to recognize place value and to add and subtract from decades.

Instructional Procedures

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Show students the number 30 in base-ten blocks. Add one ten to the number. Ask, “How many do I have now? How do you know?” Have students discuss with their partners; then call on one or two students to share.

Expect answers like “there are four 10s or 40.” Watch for students who say there are now 4. Make sure they are paying close attention to place-value vocabulary.

Repeat the process with the number 36; add one ten and ask “How many do I have now? How do you know?”

Expect answers like “four 10s and 6 ones or 46.” Watch for students who switch to 40 and have lost track of the ones.

Repeat this process with several numbers on and off the decade, adding 10 each time.

Show students the number 30 again in base-ten blocks. This time remove one 10. Ask “How many blocks do I have now? How do you know?” Have students discuss with a partner and share out.

Expect answers like “2 tens or 20.” Again watch for students who say there are 2 left. Make sure they use place-value vocabulary.

Show students the number 50 in base-ten blocks. Remove one 10. Ask “How many blocks do I have now? How do you know?” Have students discuss with their partners and then share out.

Students will use their understanding to play a game with their partners in which they add/subtract 10 from a decade number based on the roll of a number cube. One partner chooses any decade between 10 and 100 (10, 20, 30, 40, 50, 60, 70, 80, 90, or 100). The other partner rolls the number cube and either adds 10 or subtracts 10 based on the roll. Then the partners switch roles and repeat.

Extension:

Use the activities and strategies listed below to meet the needs of your students during the year.
- Routine: This could be a way to start the day, period, or activity: Simply write the date and practice adding and subtracting 10 to the number.
- Small Group: For students who need opportunities for additional learning, more practice and small-group instruction will be beneficial. Students can play the number-cube game outlined above, but with base-ten towers to use as manipulatives.
- Expansion: Students who are ready can play the number cube game, but this time the first partner chooses ANY number between 1 and 100. When ready, they can begin working on adding 10 to numbers in the hundreds.

Adding and Subtracting Within 10

Lesson Plan