Ignite Mental Math Prowess with “Let’s Find the 10s”: A Comprehensive Guide

What if I told you there was a powerful way to develop your students’ mental math skills while simultaneously making addition enjoyable and approachable? Enter “Let’s Find the 10s,” an engaging activity I’ve designed that uses long horizontal sums to explore the beauty and logic of numbers. This is your comprehensive guide to this activity, complete with detailed explanations, accommodation strategies, modifications for varying skill levels, and some exciting gameplay examples.

Introduction: The Power of 10

“Let’s Find the 10s” is based on a simple yet profound mathematical principle: the decimal system’s structure makes operations involving the number 10 significantly easier to perform mentally. This activity leverages this characteristic, challenging students to find pairs or groups of numbers in a long horizontal sum that add up to 10 or multiples of 10, making mental computation simpler and more efficient.

This activity is adaptable and versatile, working equally well as an interactive whiteboard exercise or a more traditional pen-and-paper worksheet activity. Regardless of the format, “Let’s Find the 10s” is sure to add an exciting twist to your math lessons while strengthening students’ number sense.

A Detailed Walkthrough

To illustrate the process, consider the following long horizontal sum:

3 + 11 + 7 + 5 + 5 + 4 + 9 + 1 + 2 + 13 + 8

The goal is to group numbers that total 10 or multiples of 10. Here’s one way to approach it:

We identify four pairs that yield 10: (3 + 7), (5 + 5), (9 + 1), and (2 + 8). The total of these pairs is 40. Then we have the remaining numbers: 11, 4, and 13, which sum up to 28.

Hence, the total sum is 40 + 28 = 68.

But the beauty of “Let’s Find the 10s” is that it encourages flexible thinking, allowing students to come up with several valid solutions to the same problem. For instance, a student might group the numbers this way:

First, find pairs that yield 20: (7 + 13) and (11 + 9), which gives us 40. Then, find pairs or groups that yield 10: (5 + 5) and (3 + 4 + 1 + 2), which total 20. Finally, add the lone number 8. Thus, the sum is 40 + 20 + 8 = 68, the same result as before!

Challenge your students to discover at least three different ways to group the numbers in each sum. It’s a fantastic opportunity to promote mental flexibility, creativity, and a deeper understanding of number relationships.

Accommodations and Modifications: Every Learner Matters

As educators, our primary goal is to create an inclusive learning environment that nurtures every student’s unique abilities and potential. With “Let’s Find the 10s,” there are numerous ways to accommodate learners at different levels and make the activity accessible and beneficial for all.


For students who need additional support, here are a few strategies you can employ:

  1. Chunking: Break down the long sum into smaller parts, making it easier for the student to process.
  2. Guided Practice: Work through several examples as a class before having students try independently. Model the process and thinking aloud, giving students a clear understanding of the strategy.
  3. Partner Work: Encourage students to work in pairs or small groups, promoting collaborative problem-solving.


To stretch advanced students, consider the following modifications:

  1. Increase the Length: Make the sum longer, thereby increasing the complexity of the problem.
  2. Introduce Larger Numbers: Include larger numbers in the sum to add an extra layer of challenge.
  3. Introduce Decimals: Bring decimals into the mix. This change not only ups the difficulty but also opens the door for discussions about place value and decimal operations.

Examples: Demonstrating “Let’s Find the 10s” in Action

To provide a clearer understanding of the activity, let’s explore a few more long horizontal sums and the different ways they can be grouped:

Example 1:

Consider the sum 6 + 14 + 3 + 9 + 7 + 1 + 12 + 5 + 7 + 6.

One approach might be to find pairs or groups that yield 20: (14 + 6), (9 + 7 + 1 + 3), which gives us 40. Then, find pairs that yield 10: (5 + 5), and finally add the remaining 12. So, the sum is 40 + 10 + 12 = 62.

Example 2:

For the sum 4 + 15 + 6 + 8 + 5 + 2 + 9 + 11 + 7 + 3,

You could find groups that total 20: (15 + 5), (8 + 2 + 4 + 6), which gives 40. Then, find pairs that yield 10: (9 + 1) and finally add the remaining numbers: 11 + 7 + 3, which gives 21. So, the total sum is 40 + 10 + 21 = 71.

Unleashing the Power of “Let’s Find the 10s”

In closing, “Let’s Find the 10s” is not just a mental math activity. It’s a strategic tool that nurtures number sense, promotes mental flexibility, and instills a deep understanding of the number 10’s unique characteristics in our decimal system. Whether you’re a seasoned educator or a homeschooling parent, this dynamic activity will bring a breath of fresh air to your math instruction, turning long horizontal sums into an exciting treasure hunt for 10s. So get ready, set, and start finding those 10s!

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