Doubles Minus 1 - Definition, Examples, Quiz, FAQ, Trivia
Learn to subtract quickly using the doubles minus one strategy with easy explanations and practice activities
What is Doubles Minus 1?
The doubles minus one strategy is a helpful way to solve subtraction problems when you're subtracting a number that is one less than a doubles fact. This method helps students solve problems quickly by building on what they already know about doubles.
Definition: Doubles minus one is a mental math strategy where you subtract a number from a doubles fact minus one. For example, if you know that 8 + 8 = 16, then you can use that to solve 16 - 7 because 7 is one less than 8.
Why is this strategy useful? It helps students:
- Solve subtraction problems more quickly
- Build number sense and pattern recognition
- Connect addition and subtraction concepts
- Develop mental math skills
Key Concept
If you know that A + A = 2A, then (2A) - (A - 1) = A + 1
How to Use the Doubles Minus 1 Strategy
Using the doubles minus one strategy is simple when you follow these steps:
Strategy Steps
Then A - B = C + 1
Step 2: Identify the doubles fact that is closest to the problem.
Step 3: Since you're subtracting one less than the double, the answer will be one more than the number in the double.
Let's practice with an example:
Example: Solve 12 - 5 using doubles minus one
Step 1: Notice that 5 is one less than 6 (since 6 is a doubles fact: 6 + 6 = 12)
Step 2: Think about the doubles fact: 6 + 6 = 12
Step 3: Since we're subtracting 5 (which is one less than 6), the answer is 6 + 1 = 7
So 12 - 5 = 7!
Remember
This strategy works best when the subtraction problem involves numbers that are close to doubles facts.
Examples of Doubles Minus 1
Let's look at more examples to understand how the doubles minus one strategy works:
Example 1
Doubles fact: 5 + 5 = 10
4 is one less than 5
So 10 - 4 = 5 + 1 = 6
Example 2
Doubles fact: 7 + 7 = 14
6 is one less than 7
So 14 - 6 = 7 + 1 = 8
Example 3
Doubles fact: 9 + 9 = 18
8 is one less than 9
So 18 - 8 = 9 + 1 = 10
Example 4
Doubles fact: 8 + 8 = 16
7 is one less than 8
So 16 - 7 = 8 + 1 = 9
Practice Tip
Start by memorizing doubles facts: 1+1=2, 2+2=4, 3+3=6, 4+4=8, 5+5=10, 6+6=12, 7+7=14, 8+8=16, 9+9=18, 10+10=20
Practice Quiz
Test your understanding of the doubles minus one strategy with this 5-question quiz.
Frequently Asked Questions
Here are answers to common questions about the doubles minus one strategy:
Math Trivia
Discover interesting facts about subtraction and math strategies:
Ancient Subtraction
The earliest evidence of subtraction dates back to 1800 BCE in ancient Egypt. Egyptians used a number system based on multiples of 10 and had special hieroglyphs for subtraction operations.
Brain Power
Research shows that using mental math strategies like doubles minus one strengthens neural pathways in the brain. Children who regularly practice mental math show improved working memory and problem-solving abilities.
Math Facts Record
The world record for solving 100 subtraction problems is 1 minute 18 seconds! Most people can solve problems much faster using strategies like doubles minus one than by counting on their fingers.
Pattern Recognition
Math strategies like doubles minus one help children recognize patterns in numbers. This pattern recognition skill transfers to other areas like music, language, and problem-solving in science.
