Solve Decimal Multiplication: 0.4 × 115

Q: Why can't I just multiply 115 × 4 and get 460?

Because 0.4 is not the same as 4! The decimal point means you're multiplying by four-tenths, not four whole units. You need to account for that decimal place in your final answer.

Q: What's the easiest way to multiply by 0.4?

Think of $ 0.4 $ as "4 tenths" or $ \frac{4}{10} $. Multiply by 4 first: $ 115 \times 4 = 460 $, then divide by 10: $ 460 ÷ 10 = 46 $.

Q: How do I know where to put the decimal point?

Count the decimal places in both numbers you're multiplying. Since 0.4 has 1 decimal place and 115 has 0, your answer should have 1 decimal place. But 46 is a whole number, so no decimal point needed!

Q: Can I use a different method to solve this?

Yes! You could also think of it as $ 115 ÷ 10 \times 4 = 11.5 \times 4 = 46 $, or use the standard algorithm. All methods should give you the same answer: 46.

Decimal Multiplication with Three-Digit Integers

$0.4\times115=$

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations

00:00 Solve

00:03 Multiply each digit by each digit, and place in the appropriate position

00:10 Calculate and place, add the tens digit when needed

00:22 Move to the next digit, calculate and place in the appropriate position

00:29 Any number multiplied by 1 always equals itself

00:37 Move to the next digit, calculate and place in the appropriate position

00:42 Connect the results

00:47 Sum up the digits after the decimal point

00:50 Based on this sum, place the decimal point

00:55 And this is the solution to the question

Step-by-step written solution

Follow each step carefully to understand the complete solution

Understand the problem

$0.4\times115=$

Step-by-step solution

To solve this problem, we need to calculate the product of $0.4$ and $115$ .

First, let's perform the multiplication:

Multiply $115$ by $0.4$ :

115 \times 0.4 = 46

Here's how the calculation works step-by-step:

Consider $0.4$ as $\frac{4}{10}$ .
Therefore, the multiplication becomes $115 \times \frac{4}{10}$ .
Perform the multiplication first: $115 \times 4 = 460$ .
Then divide by $10$ to manage the decimal place: $\frac{460}{10} = 46$ .

Thus, the solution to the problem is $46$ .

Final Answer

$46$

Key Points to Remember

Essential concepts to master this topic

Rule: Treat decimal as fraction to understand place value positioning
Technique: Convert $0.4$ to $\frac{4}{10}$ , then $115 \times 4 ÷ 10 = 46$
Check: Count decimal places: 0.4 has 1, so $460 ÷ 10 = 46$ ✓

Common Mistakes

Avoid these frequent errors

Forgetting to handle the decimal place
Don't multiply 115 × 4 = 460 and leave it as your final answer! This ignores the decimal and gives 460 instead of 46. Always count decimal places in the original problem and apply them to your result.

Practice Quiz

Test your knowledge with interactive questions

$\text{0}.07\times10=$

FAQ

Everything you need to know about this question

Why can't I just multiply 115 × 4 and get 460?

Because 0.4 is not the same as 4! The decimal point means you're multiplying by four-tenths, not four whole units. You need to account for that decimal place in your final answer.

What's the easiest way to multiply by 0.4?

Think of $0.4$ as "4 tenths" or $\frac{4}{10}$ . Multiply by 4 first: $115 \times 4 = 460$ , then divide by 10: $460 ÷ 10 = 46$ .

How do I know where to put the decimal point?

Count the decimal places in both numbers you're multiplying. Since 0.4 has 1 decimal place and 115 has 0, your answer should have 1 decimal place. But 46 is a whole number, so no decimal point needed!

Can I use a different method to solve this?

Yes! You could also think of it as $115 ÷ 10 \times 4 = 11.5 \times 4 = 46$ , or use the standard algorithm. All methods should give you the same answer: 46.

What if I get a decimal in my final answer?

That's totally normal! Many decimal multiplications result in decimal answers. Just make sure you've counted decimal places correctly and your answer makes sense in the context.

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