What is a Rule Using 'multiply by'?

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Grade Level:

Class 4

All STEM domains, Finance, Economics, Data Science, AI, Physics, Chemistry

Definition

What is it?

A rule using 'multiply by' tells us to find a new number by taking an original number and multiplying it by a specific value. It's like a special instruction that always uses multiplication to change a number into another number.

Simple Example

Quick Example

Imagine a shopkeeper sells samosas for ₹10 each. If you want to know the total cost for any number of samosas, the rule is 'multiply the number of samosas by 10'. So, if you buy 3 samosas, the cost is 3 x 10 = ₹30.

Worked Example

Step-by-Step

Let's say a rule is 'multiply by 5'. We need to find the output for the input number 7.
1. Identify the input number: The input number is 7.
2. Identify the rule: The rule is 'multiply by 5'.
3. Apply the rule: Multiply the input number (7) by the given multiplier (5).
4. Calculation: 7 x 5 = 35.
5. State the output: The output is 35. So, if the input is 7 and the rule is 'multiply by 5', the output is 35.

Why It Matters

Understanding 'multiply by' rules is key to solving problems in many fields. Engineers use it to scale designs, scientists use it for calculations in experiments, and economists use it to understand how prices change. It's a foundational skill for careers in technology, finance, and research.

Common Mistakes

MISTAKE: Adding the number instead of multiplying. For example, if the rule is 'multiply by 3' and the input is 4, a student might do 4 + 3 = 7. | CORRECTION: Always perform multiplication as stated in the rule. For 'multiply by 3' with input 4, it should be 4 x 3 = 12.

MISTAKE: Multiplying the rule number by the input number, instead of the input by the rule number. For example, if the rule is 'multiply by 6' and the input is 2, a student might think 6 x 2 means '6 is the input'. | CORRECTION: The input number is always the one being changed. So, it's Input x Multiplier. For input 2 and rule 'multiply by 6', it's 2 x 6 = 12.

MISTAKE: Confusing 'multiply by' with 'times'. While they mean the same, sometimes students get confused if they see 'times 3' versus 'multiply by 3'. | CORRECTION: Both 'multiply by 3' and 'times 3' mean the same operation. Just remember it means repeated addition or finding the product.

Practice Questions

Try It Yourself

QUESTION: If the rule is 'multiply by 4', what is the output for the input 9? | ANSWER: 36

QUESTION: A baker makes laddus. For every 1 kg of flour, he can make 12 laddus. What is the rule to find the number of laddus? If he uses 5 kg of flour, how many laddus can he make? | ANSWER: Rule: 'multiply by 12'. Number of laddus: 60.

QUESTION: A taxi charges ₹15 per kilometer. If you travel 8 kilometers, what is the total fare? What if you also have to pay a fixed charge of ₹20? | ANSWER: Total fare for 8 km: 8 x 15 = ₹120. Total fare including fixed charge: 120 + 20 = ₹140.

MCQ

Quick Quiz

What is the output if the input is 6 and the rule is 'multiply by 7'?

The Correct Answer Is:

The rule 'multiply by 7' means we take the input number (6) and multiply it by 7. So, 6 x 7 = 42. Options A, C, and D are incorrect as they result from addition, division, or incorrect placement.

Real World Connection

In the Real World

When you buy items online, like from Flipkart or Amazon, the total bill is calculated using a 'multiply by' rule for each item's quantity and price. Even when calculating how much data you use on your phone, if 1 GB costs a certain amount, the total cost for 3 GB is found by multiplying.

Key Vocabulary

Key Terms

RULE: A set instruction to follow | INPUT: The starting number we apply the rule to | OUTPUT: The new number we get after applying the rule | MULTIPLY: To perform the operation of multiplication, which is repeated addition | PRODUCT: The result of multiplication

What's Next

What to Learn Next

Next, you can explore 'What is a Rule Using 'divide by'?' and then 'What is a Rule Using 'add to'?' These concepts will help you understand how different operations create patterns and change numbers, which is crucial for algebra.