What is Adding Near Doubles?

S1-SA1-0054

Grade Level:

Class 2

Maths, Computing

Definition

What is it?

Adding Near Doubles is a mental math strategy where you add two numbers that are very close to each other. Instead of adding them directly, you double the smaller number and then add the small difference, or double the larger number and subtract the small difference. It makes calculations faster and easier in your head.

Simple Example

Quick Example

Imagine you bought two packets of biscuits. One packet has 8 biscuits and the other has 9 biscuits. Instead of counting 8 + 9 directly, you can think: '8 + 8 = 16, and then add 1 more for the extra biscuit in the second packet.' So, 16 + 1 = 17 biscuits.

Worked Example

Step-by-Step

Let's add 12 + 13 using the Near Doubles strategy.

1. Identify the two numbers: 12 and 13.
---2. See that they are very close. 13 is just 1 more than 12.
---3. Double the smaller number: 12 + 12 = 24.
---4. Now, add the difference. Since 13 is 1 more than 12, add 1 to the doubled sum: 24 + 1 = 25.
---5. So, 12 + 13 = 25.

Why It Matters

Understanding Near Doubles helps you solve math problems much faster in your head, which is useful for quick calculations in daily life. This skill is a building block for more complex arithmetic and is essential for careers in finance, engineering, and even software development where quick mental math is often needed.

Common Mistakes

MISTAKE: Forgetting to add the difference after doubling. For 7 + 8, students might just say 7 + 7 = 14. | CORRECTION: Always remember to add (or subtract) the difference between the two numbers after doubling. For 7 + 8, it's 7 + 7 + 1 = 15.

MISTAKE: Doubling the larger number and then adding the difference. For 7 + 8, students might do 8 + 8 = 16, then add 1. | CORRECTION: While this can work, it's usually simpler to double the smaller number and add the difference. Or, if you double the larger, you must subtract the difference. For 7 + 8, it's 8 + 8 - 1 = 15.

MISTAKE: Applying Near Doubles when numbers are not close. For 5 + 10, trying to use Near Doubles. | CORRECTION: This strategy works best when numbers are 'near doubles' – typically differing by 1 or 2. For numbers far apart, use other addition strategies.

Practice Questions

Try It Yourself

QUESTION: Use Near Doubles to solve 6 + 7. | ANSWER: 6 + 6 = 12, then 12 + 1 = 13.

QUESTION: An auto-rickshaw driver completed two trips. One trip was 15 km and the next was 16 km. How many total kilometers did he travel using the Near Doubles strategy? | ANSWER: 15 + 15 = 30, then 30 + 1 = 31 km.

QUESTION: Your mom bought two sets of diyas for Diwali. One set had 19 diyas and the other had 20 diyas. What is the total number of diyas? Explain how you would use Near Doubles. | ANSWER: 19 + 19 = 38. Since 20 is 1 more than 19, add 1 to 38. So, 38 + 1 = 39 diyas.

MCQ

Quick Quiz

Which of these sums is best solved using the Near Doubles strategy?

5 + 15

8 + 9

2 + 10

3 + 20

The Correct Answer Is:

Option B (8 + 9) is correct because 8 and 9 are 'near doubles' – they differ by only 1. The other options have numbers that are too far apart for this strategy to be efficient.

Real World Connection

In the Real World

When you are calculating your total mobile data usage for two days, say 1.8 GB on Monday and 1.9 GB on Tuesday, you can quickly estimate using near doubles (1.8 + 1.8 + 0.1). Similarly, shopkeepers use this when quickly adding up prices of two items that are very similar, like two packets of chips costing Rs 10 and Rs 11.

Key Vocabulary

Key Terms

NEAR DOUBLES: Numbers that are close to each other, typically differing by 1 or 2 | MENTAL MATH: Solving math problems in your head without writing them down | STRATEGY: A plan or method used to solve a problem | DIFFERENCE: The result of subtracting one number from another

What's Next

What to Learn Next

Great job learning Near Doubles! Next, you can explore 'Adding by Making a Ten'. This strategy also helps you add numbers quickly by finding pairs that sum up to 10, building on your mental math skills even further.