What is Multiplication Before Subtraction (BODMAS)?

S1-SA1-0180

Grade Level:

Class 5

Maths, Computing, Programming, AI

Definition

What is it?

Multiplication Before Subtraction is a rule that tells you which operation to do first when you see both multiplication and subtraction in the same maths problem. It's part of the BODMAS (or PEMDAS) order of operations, meaning you always multiply before you subtract to get the correct answer.

Simple Example

Quick Example

Imagine you buy 3 packets of biscuits, and each packet costs ₹10. You pay with a ₹50 note. To find out how much change you get, you first multiply the number of packets by their price (3 x ₹10 = ₹30), and then subtract that total from the money you paid (₹50 - ₹30). If you subtract first, you'd get the wrong answer!

Worked Example

Step-by-Step

Let's solve: 20 - 3 x 4

Step 1: Identify the operations. We have subtraction (-) and multiplication (x).

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Step 2: According to the 'Multiplication Before Subtraction' rule (BODMAS), we must do multiplication first.

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Step 3: Perform the multiplication: 3 x 4 = 12.

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Step 4: Now, substitute the result back into the problem: 20 - 12.

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Step 5: Perform the subtraction: 20 - 12 = 8.

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Answer: The correct answer is 8.

Why It Matters

Understanding this order is crucial for solving complex maths problems correctly, whether you're calculating finances or designing software. It's a fundamental concept in computing and programming, where computers need precise instructions to perform calculations, and even in fields like AI for processing data accurately.

Common Mistakes

MISTAKE: Solving operations from left to right without considering the rule (e.g., 10 - 2 x 3 = 8 x 3 = 24) | CORRECTION: Always do multiplication first, then subtraction (10 - (2 x 3) = 10 - 6 = 4).

MISTAKE: Confusing the order with addition (e.g., thinking subtraction comes before addition, which it doesn't in BODMAS if they are at the same level) | CORRECTION: Remember BODMAS: Brackets, Orders (powers/roots), Division/Multiplication (left to right), Addition/Subtraction (left to right).

MISTAKE: Forgetting that the multiplication rule applies even if the multiplication sign is hidden (e.g., 5 - 2(3) where 2(3) means 2 x 3) | CORRECTION: Always treat numbers next to brackets as multiplication unless another operation is explicitly shown.

Practice Questions

Try It Yourself

QUESTION: Solve: 15 - 2 x 5 | ANSWER: 5

QUESTION: A vendor has 30 samosas. He sells 4 plates, and each plate has 3 samosas. How many samosas are left? | ANSWER: 18

QUESTION: Evaluate: 50 - 5 x 6 + 2 x 4 (Hint: Do all multiplications first, then subtract/add from left to right) | ANSWER: 28

MCQ

Quick Quiz

Which operation should you perform first in the expression 25 - 4 x 5?

Subtraction

Multiplication

It doesn't matter

Add 25 and 4

The Correct Answer Is:

According to the BODMAS rule, multiplication always comes before subtraction. So, you must calculate 4 x 5 first.

Real World Connection

In the Real World

When you use a calculator app on your phone or computer, it automatically follows the BODMAS rule to give you the correct answer. For example, if you type '100 - 5 * 10' into Google Search, it will correctly show 50, not 950, because it multiplies 5 by 10 first. This rule is vital for engineers at ISRO calculating rocket trajectories or for financial analysts managing budgets.

Key Vocabulary

Key Terms

BODMAS: An acronym for Brackets, Orders, Division, Multiplication, Addition, Subtraction, which defines the order of operations | OPERATION: A mathematical process like addition, subtraction, multiplication, or division | EXPRESSION: A mathematical phrase that can contain numbers, variables, and operations | ORDER OF OPERATIONS: The specific sequence in which mathematical operations must be performed to solve an expression correctly

What's Next

What to Learn Next

Great job mastering multiplication before subtraction! Next, you should explore the full BODMAS rule, which includes brackets, division, and addition. Understanding the complete order will help you solve even more complex problems with confidence.