Calculate the Specific Percentage: What is 40% of 70?

Q: Why do I need to divide by 100 to convert a percentage?

Because percent means 'per hundred'! When you see 40%, it really means 40 out of 100, or $\frac{40}{100}$ = 0.4 as a decimal.

Q: Can I use a fraction instead of a decimal?

Absolutely! You can write 40% as $\frac{40}{100} = \frac{2}{5}$. Then calculate: $\frac{2}{5} \times 70 = \frac{140}{5} = 28$. Both methods give the same answer!

Q: What's the easiest way to remember this process?

Think: 'Percent to decimal, then multiply!' Just move the decimal point two places left (40% becomes 0.40), then multiply by your number.

Q: How can I check if my percentage calculation is reasonable?

Use mental math! 40% is close to half (50%), so 40% of 70 should be a bit less than 35. Since 28

Q: What if I get a decimal answer instead of a whole number?

That's completely normal! Many percentage problems result in decimals. For example, 40% of 75 would be $0.4 \times 75 = 30$, but 40% of 73 would be $0.4 \times 73 = 29.2$.

Step-by-step video solution

Watch the teacher solve the problem with clear explanations

00:00 Calculate 40% of 70

00:03 Use the formula to convert a percentage into a fraction

00:07 This fraction is equal to 40%

00:16 Multiply this fraction by the number itself in order to determine the percentage

00:25 Factor and reduce wherever possible

00:32 Here is the solution

Step-by-step written solution

Follow each step carefully to understand the complete solution

1

Understand the problem

Calculate 40% of 70:

2

Step-by-step solution

To solve this problem, we will follow these steps:

Step 1: Convert the percentage to a decimal.
Step 2: Multiply the resulting decimal by the whole number to find the desired quantity.

Now, let's work through these steps in detail:

Step 1: Convert the percentage to a decimal form.
The given percentage is 40%. As a decimal, 40% is converted by dividing by 100:
$\frac{40}{100} = 0.4$ .

Step 2: Multiply the decimal by the whole number.
We now multiply the decimal $0.4$ with the whole number $70$ :
$0.4 \times 70 = 28$ .

Therefore, 40% of 70 is $28$ .

3

Final Answer

28

Key Points to Remember

Essential concepts to master this topic

Rule: Convert percentage to decimal by dividing by 100
Technique: Multiply decimal by whole number: 0.4 × 70 = 28
Check: Verify by dividing result by original: 28 ÷ 70 = 0.4 = 40% ✓

Common Mistakes

Avoid these frequent errors

Forgetting to convert percentage to decimal
Don't multiply 40 × 70 = 2,800! This treats the percentage as a whole number and gives a result 100 times too large. Always convert the percentage to a decimal first by dividing by 100.

Practice Quiz

Test your knowledge with interactive questions

Calculate 30 over 100 as a percentage:

FAQ

Everything you need to know about this question

Why do I need to divide by 100 to convert a percentage?

+

Because percent means 'per hundred'! When you see 40%, it really means 40 out of 100, or $\frac{40}{100}$ = 0.4 as a decimal.

Can I use a fraction instead of a decimal?

+

Absolutely! You can write 40% as $\frac{40}{100} = \frac{2}{5}$ . Then calculate: $\frac{2}{5} \times 70 = \frac{140}{5} = 28$ . Both methods give the same answer!

What's the easiest way to remember this process?

+

Think: 'Percent to decimal, then multiply!' Just move the decimal point two places left (40% becomes 0.40), then multiply by your number.

How can I check if my percentage calculation is reasonable?

+

Use mental math! 40% is close to half (50%), so 40% of 70 should be a bit less than 35. Since 28 < 35, our answer makes sense!

What if I get a decimal answer instead of a whole number?

+

That's completely normal! Many percentage problems result in decimals. For example, 40% of 75 would be $0.4 \times 75 = 30$ , but 40% of 73 would be $0.4 \times 73 = 29.2$ .

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