What is Counting On to Subtract?

S1-SA1-0074

Grade Level:

Class 2

Maths, Computing

Definition

What is it?

Counting On to Subtract is a simple way to find the difference between two numbers. Instead of taking away, you start from the smaller number and count up to the bigger number, keeping track of how many steps you took. This number of steps is your answer.

Simple Example

Quick Example

Imagine you have 7 ladoos and your friend has 10 ladoos. To find out how many more ladoos your friend has, you can start from 7 and count up: 8 (1), 9 (2), 10 (3). Your friend has 3 more ladoos.

Worked Example

Step-by-Step

Let's subtract 12 from 18 using counting on.

Step 1: Identify the smaller number and the larger number. Smaller number is 12, larger number is 18.
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Step 2: Start counting from the smaller number (12).
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Step 3: Count up to the larger number (18), keeping track of your counts.
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Step 4: From 12, we count: 13 (1), 14 (2), 15 (3), 16 (4), 17 (5), 18 (6).
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Step 5: We counted 6 steps.
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So, 18 - 12 = 6.

Why It Matters

Understanding counting on helps build a strong foundation for mental math, which is super useful in everyday life. It's a basic skill that helps in problem-solving and is even used in computer programming to calculate differences or steps. Future engineers and data scientists use these logical steps all the time!

Common Mistakes

MISTAKE: Starting to count from the larger number | CORRECTION: Always start counting from the smaller number and count up to the larger number.

MISTAKE: Forgetting to count the first 'jump' from the smaller number | CORRECTION: When you count, the first number you say after the smaller number is your first 'count'. For example, from 7 to 10: 8 (1), 9 (2), 10 (3).

MISTAKE: Counting the starting number itself | CORRECTION: Do not count the smaller number you are starting from. Start counting from the number *after* it.

Practice Questions

Try It Yourself

QUESTION: Use counting on to subtract 9 from 15. | ANSWER: 6

QUESTION: A bus has 14 passengers. At the next stop, 21 passengers get on in total. How many more passengers got on than were already there? Use counting on. | ANSWER: 7

QUESTION: You have 23 stickers. Your friend has 30 stickers. How many more stickers does your friend have? Show your counting on steps. | ANSWER: 7 (24 (1), 25 (2), 26 (3), 27 (4), 28 (5), 29 (6), 30 (7))

MCQ

Quick Quiz

Which of these shows the correct way to use counting on to find 20 - 16?

Count from 20 to 16

Count from 16 to 20: 17 (1), 18 (2), 19 (3), 20 (4)

Count from 16 to 20: 16 (1), 17 (2), 18 (3), 19 (4), 20 (5)

Count from 20 and subtract 16

The Correct Answer Is:

Option B correctly starts from the smaller number (16) and counts up to the larger number (20), tracking the jumps. Options A and D are incorrect methods for counting on, and Option C incorrectly counts the starting number.

Real World Connection

In the Real World

When you are shopping at a local kirana store and buy items worth Rs 45, and you give the shopkeeper Rs 50, they often 'count on' to give you change. They might say '45... and 5 makes 50', giving you Rs 5 back. This is exactly how counting on works!

Key Vocabulary

Key Terms

DIFFERENCE: The result of subtracting one number from another | COUNT ON: A strategy to subtract by counting up from the smaller number to the larger number | MENTAL MATH: Doing calculations in your head without writing them down | SUBTRACTION: The process of taking one number away from another

What's Next

What to Learn Next

Great job learning counting on! Next, you can explore other subtraction strategies like 'breaking apart' numbers or using a number line. These methods will help you subtract even bigger numbers more easily.