Mental Subtraction

Contributor: Rachel Lewis. Lesson ID: 12180

Where is your best calculator? Is it in your pocket, desk, computer, or smartphone? Sometimes, your best math partner is in your head! Learn these easy subtraction tricks for when you are on your own!

categories

Elementary

subject
Math
learning style
Kinesthetic, Visual
personality style
Otter, Beaver
Grade Level
Intermediate (3-5)
Lesson Type
Skill Sharpener

Lesson Plan - Get It!

Audio:

Oh no! You have to figure out 79 minus 85! You have no blackboard or whiteboard or pencil or paper, or even a smartphone! Can you figure this out? You can if you use mental math!

What is the answer to 4 minus 2?

If you said 2, then you are correct!

How did you find the difference? Did you work out 4 minus 2 on a piece of paper? Did you count on your fingers, or did you figure it out in your head?

When you solve a math problem in your head without help from calculators, computers, or pencil and paper, you are doing mental math.

4 minus 2 can be quickly solved using just your brain, but what about 52 minus 34?

There are many different strategies to help you subtract two numbers with metal math.

You can subtract parts using the tens and ones place value:

  • Think:
    52 – 30 – 4 = 18

You can "add backwards":

  • Think:
    34 + _____ = 52

You can round the number, then correct the answer:

  • Think:
    52 - 30 = 22
    22 – 4 = 18

Review more tips and tricks to subtract numbers at Mental Subtraction Strategies (homeschoolmath.net). Read the strategies and examples and try the practice problems.

What are some of the tricks you learned? Share them with your parent or teacher. Discuss how you can subtract in parts, use subtraction facts, and add up to find the difference.

Next, go to the Got It? section to play a mental subtraction game!

Elephango's Philosophy

We help prepare learners for a future that cannot yet be defined. They must be ready for change, willing to learn and able to think critically. Elephango is designed to create lifelong learners who are ready for that rapidly changing future.