Mentally Add/Subtract Using 10 and 100


In our Mentally Add/Subtract Using 10 and 100s lesson plan, students learn how to easily add or subtract 10 or 100 to or from a number. Students practice using this skill, strengthening their mental math abilities.

Included with this lesson are some adjustments or additions that you can make if you’d like, found in the “Options for Lesson” section of the Classroom Procedure page. One of the optional additions to this lesson is to have more advanced students use numbers with higher place values, like thousands and ten-thousands.

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What our Mentally Add/Subtract Using 10 and 100 lesson plan includes

Lesson Objectives and Overview: Mentally Add/Subtract Using 10 and 100 lesson plan introduces students to strategies they can use to add and subtract larger numbers with ease. The topic is introduced using charts, so students have a visual to aide their understanding. At the end of the lesson, students will be able to mentally add and subtract 10 and 100 using numbers from 0 to 999. This lesson is for students in 1st grade and 2nd grade.

Classroom Procedure

Every lesson plan provides you with a classroom procedure page that outlines a step-by-step guide to follow. You do not have to follow the guide exactly. The guide helps you organize the lesson and details when to hand out worksheets. It also lists information in the blue box that you might find useful. You will find the lesson objectives, state standards, and number of class sessions the lesson should take to complete in this area. In addition, it describes the supplies you will need as well as what and how you need to prepare beforehand. You don’t need any supplies for this lesson. To prepare for this lesson ahead of time, you can create the bags of numbers and bags of equations for the activity and copy the handouts.

Options for Lesson

Included with this lesson is an “Options for Lesson” section that lists a number of suggestions for activities to add to the lesson or substitutions for the ones already in the lesson. One optional adjustment for more advanced students is to have them use numbers with higher place values, like thousands and ten-thousands. For an additional activity, students could create their own thousands board to help with adding and subtracting 100 at the beginning of the lesson. You could also create a fun matching game with cards. Finally, students could write scenarios where they would need to add or subtract 10 or 100.

Teacher Notes

The teacher notes page includes lines that you can use to add your own notes as you’re preparing for this lesson.


Mentally Add and Subtract 10

The Mentally Add/Subtract Using 10 and 100 lesson plan includes three pages of content. The lesson begins by reminding students that math is full of patterns. Some patterns are helpful for solving math problems with addition and subtraction in our heads. This can save a lot of time while doing math.

Adding or subtracting 10 is one pattern. Once you learn it, you’ll be able to easily add or subtract 10 to or from any number. The lesson illustrates this pattern using a hundreds chart. To add 10 to a number, you simply move down one row on the chart. To subtract, you move up one row. The lesson shows examples of both of these. You can also add one to the tens place of the number to add 10, and subtract one from the tens place to subtract 10. For example, to add 10 to 26, you can just add 1 to the 2 to get 36. To subtract 10 from 58, you would subtract 1 from the 5 to get 48.

You can start out by using the hundreds chart, but once you understand the pattern, you won’t need to use it anymore! Simply add or subtract one from the tens place.

Mentally Add and Subtract 100

Adding or subtracting 100 is a similar process. You could use a thousands chart, but we don’t usually have a thousands chart with us. Instead, we can solve these problems in our head using a similar method to the one used for adding and subtracting 10.

If we want to add 100 to the number 642, we can first break 642 down into 6 hundreds, 4 tens, and 2 ones. To add 100, we simply add one to the hundreds place (like we did with the tens place to add 10). Therefore, 642 + 100 = 742. Note that the tens and ones places did not change in value, only the hundreds.

For subtraction, we simply subtract one from the hundreds place. To subtract 100 from the number 389, for example, we can identify the hundreds place (3) and subtract one. Therefore, 389 – 100 = 289. Again, the tens and ones places did not change in value.


The Mentally Add/Subtract Using 10 and 100 lesson plan includes four worksheets: an activity worksheet, a practice worksheet, a homework assignment, and a quiz. You can refer to the guide on the classroom procedure page to determine when to hand out each worksheet.


Students will work in groups of four or fewer to complete this activity. Each group receives two bags, one of which contains a set of random numbers; the other contains equations. Students will individually draw numbers and equations to create math sentences to solve. They will solve the problems mentally on the provided recording sheet.


For the practice worksheet, students will first cut out the numbers at the bottom of the worksheet. They will then glue them in the correct answer spaces. For example, they would glue the number 120 in the answer space next to 110, Add 10.


The homework assignment asks students to solve 20 problems using mental math. They will solve problems where they have to add 10, subtract 10, add 100, and subtract 100.


This lesson includes a quiz that you can use to test students’ knowledge and understanding of the lesson material. The quiz asks them to use mental math to find solutions to five problems.

Worksheet Answer Keys

This lesson plan includes answer keys for the practice worksheet,  the homework assignment, and the quiz. If you choose to administer the lesson pages to your students via PDF, you will need to save a new file that omits these pages. Otherwise, you can simply print out the applicable pages and keep these as reference for yourself when grading assignments.

Additional information


1st Grade, 2nd Grade



State Educational Standards

LB.Math.Content.1.NBT.B.8, LB.Math.Content.2.NBT.C.5

Lessons are aligned to meet the education objectives and goals of most states. For more information on your state objectives, contact your local Board of Education or Department of Education in your state.