Inaugurated by IN-SPACe
ISRO Registered Space Tutor
S1-SA2-0275
What is Multiplying a Decimal by a Whole Number?
Grade Level:
Class 5
Maths, Finance, Science, Computing, AI
Definition
What is it?
Multiplying a decimal by a whole number means finding the total amount when a decimal value is repeated a certain number of times. It's like adding the same decimal number over and over, but multiplication is a quicker way to do it.
Simple Example
Quick Example
Imagine one samosa costs Rs 12.50. If you want to buy 3 samosas, how much will you pay? Here, you are multiplying the decimal price (Rs 12.50) by the whole number of samosas (3) to find the total cost.
Worked Example
Step-by-Step
Let's multiply 4.75 by 6.
1. Ignore the decimal point for a moment and multiply the numbers as if they were whole numbers: 475 x 6.
---
2. Multiply the ones digit: 6 x 5 = 30. Write down 0, carry over 3.
---
3. Multiply the tens digit: 6 x 7 = 42. Add the carried over 3: 42 + 3 = 45. Write down 5, carry over 4.
---
4. Multiply the hundreds digit: 6 x 4 = 24. Add the carried over 4: 24 + 4 = 28. Write down 28.
---
5. So, 475 x 6 = 2850.
---
6. Now, count the number of decimal places in the original decimal number (4.75). There are two digits after the decimal point.
---
7. Place the decimal point in your answer (2850) so that there are the same number of decimal places. Starting from the right, move the decimal point two places to the left.
---
8. The answer is 28.50.
Answer: 28.50
Why It Matters
This skill is super useful in everyday life and future studies! From calculating your monthly mobile bill to understanding scientific measurements or even managing finances, multiplying decimals is key. It's used by scientists, shopkeepers, and even software developers to ensure calculations are precise.
Common Mistakes
MISTAKE: Forgetting to count the decimal places in the original decimal number. | CORRECTION: Always count the total number of digits after the decimal point in the decimal number you are multiplying.
MISTAKE: Placing the decimal point incorrectly in the final answer. | CORRECTION: The number of decimal places in the product must be exactly the same as the number of decimal places in the original decimal factor.
MISTAKE: Multiplying the decimal point itself. | CORRECTION: Treat the numbers as whole numbers during multiplication, then reintroduce the decimal point at the very end based on the count of decimal places.
Practice Questions
Try It Yourself
QUESTION: A small packet of biscuits weighs 0.15 kg. What is the total weight of 5 such packets? | ANSWER: 0.75 kg
QUESTION: If a tailor uses 2.25 meters of cloth for one shirt, how much cloth will he need for 7 shirts? | ANSWER: 15.75 meters
QUESTION: An auto-rickshaw charges Rs 15.75 per kilometer. If you travel 12 kilometers, how much will the fare be? | ANSWER: Rs 189.00
MCQ
Quick Quiz
What is 3.4 x 8?
2.72
27.2
272
0.272
The Correct Answer Is:
B
Multiplying 34 by 8 gives 272. Since 3.4 has one decimal place, the answer must also have one decimal place, making it 27.2.
Real World Connection
In the Real World
When you buy vegetables at the market, if tomatoes cost Rs 35.50 per kg and you buy 2 kg, the vendor quickly calculates the total using this concept. Similarly, when calculating fuel costs for a long drive based on price per litre and litres filled, you're using decimal multiplication.
Key Vocabulary
Key Terms
DECIMAL: A number that includes a decimal point, representing parts of a whole | WHOLE NUMBER: A number without fractions or decimals, like 0, 1, 2, 3... | PRODUCT: The answer to a multiplication problem | DECIMAL PLACE: The position of a digit to the right of the decimal point.
What's Next
What to Learn Next
Great job mastering this! Next, you can learn about 'Multiplying a Decimal by a Decimal'. This will help you calculate even more complex real-world problems, like finding the area of a room with decimal dimensions.
