What is Subtracting Three-Digit Numbers?

S1-SA1-0071

Grade Level:

Class 3

Maths, Computing, Finance

Definition

What is it?

Subtracting three-digit numbers means finding the difference between two numbers, each having hundreds, tens, and ones places. It helps us figure out how much is left when we take one quantity away from another, especially when dealing with larger numbers.

Simple Example

Quick Example

Imagine you have Rs. 550 saved for a new cricket bat. If the bat costs Rs. 320, how much money will you have left after buying it? To find out, you would subtract 320 from 550.

Worked Example

Step-by-Step

Let's subtract 435 from 789.

Step 1: Write the numbers one below the other, aligning the ones, tens, and hundreds places.
789
- 435
-----

Step 2: Subtract the ones digits. 9 - 5 = 4. Write 4 in the ones place of the answer.
789
- 435
-----
4

Step 3: Subtract the tens digits. 8 - 3 = 5. Write 5 in the tens place of the answer.
789
- 435
-----
54

Step 4: Subtract the hundreds digits. 7 - 4 = 3. Write 3 in the hundreds place of the answer.
789
- 435
-----
354

So, 789 - 435 = 354.

Why It Matters

Subtracting three-digit numbers is essential for managing money, calculating distances, and understanding statistics. People in finance use it to balance budgets, engineers use it to calculate material differences, and even data analysts use it to compare figures.

Common Mistakes

MISTAKE: Subtracting the smaller digit from the larger digit regardless of its position (e.g., in 523 - 341, doing 4-2 instead of borrowing) | CORRECTION: Always subtract the bottom digit from the top digit. If the top digit is smaller, you must 'borrow' from the digit to its left.

MISTAKE: Forgetting to adjust the digit from which you borrowed (e.g., borrowing from 7 to make 6, but still using 7 for the next subtraction) | CORRECTION: When you borrow 1 from a digit, remember to reduce that digit by 1 before performing the next subtraction.

MISTAKE: Not aligning the numbers correctly by place value (ones under ones, tens under tens, hundreds under hundreds) | CORRECTION: Always write the numbers one below the other, making sure the ones, tens, and hundreds digits are in their correct columns.

Practice Questions

Try It Yourself

QUESTION: A library had 875 storybooks. They gave away 230 books to a school. How many books are left in the library? | ANSWER: 645 books

QUESTION: Your school bus travels 612 km in a week. If it covered 345 km in the first three days, how many kilometers did it cover in the remaining days? | ANSWER: 267 km

QUESTION: A farmer harvested 930 kg of potatoes. He sold 485 kg in the market and gave 120 kg to his neighbours. How many kilograms of potatoes does he have left? | ANSWER: 325 kg

MCQ

Quick Quiz

What is the difference between 700 and 456?

244

356

254

344

The Correct Answer Is:

To find 700 - 456, you need to borrow. 700 becomes 6 hundreds, 9 tens, and 10 ones. Then, 10 - 6 = 4, 9 - 5 = 4, and 6 - 4 = 2. So, the answer is 244.

Real World Connection

In the Real World

When you check your mobile data usage, you might see you started with 1024 MB and have used 350 MB. To know how much data is left, your phone's system uses subtraction of three-digit (or more) numbers. Similarly, shopkeepers use it to calculate change after a customer pays.

Key Vocabulary

Key Terms

SUBTRACTION: Taking one number away from another to find the difference | DIFFERENCE: The result of subtracting one number from another | BORROWING: A technique used in subtraction when a digit in the minuend is smaller than the corresponding digit in the subtrahend | PLACE VALUE: The value of each digit in a number based on its position (ones, tens, hundreds)

What's Next

What to Learn Next

Great job mastering subtraction of three-digit numbers! Next, you can explore 'Subtraction with Larger Numbers' or 'Subtraction of Decimals'. These concepts build on your understanding of place value and borrowing, making you even better at solving real-world math problems.