Calculate 2/5 of 40: Finding Girls in a First Grade Class

Q: Why do I multiply instead of divide when finding a fraction of a number?

"Of" means multiply in math! When you see "2/5 of 40," it's asking for 2/5 × 40. Think of it as taking 2 parts out of every 5 parts of the 40 students.

Q: Can I solve this a different way?

Yes! You can think of it as: First find 1/5 of 40 = 8 students, then multiply by 2 to get 2/5 of 40 = 16 students. Both methods give the same answer!

Q: What if the fraction doesn't divide evenly?

Sometimes you might get a decimal or mixed number! For example, $ \frac{2}{5} $ of 41 would give 16.4, which you'd need to round appropriately since you can't have partial people.

Q: Do I always multiply the whole number by the numerator first?

Yes! The order is: whole number × numerator, then ÷ denominator. This prevents errors and keeps your work organized. You can also think of it as $ \frac{\text{whole} \times \text{numerator}}{\text{denominator}} $.

Fraction Multiplication with Whole Numbers

In 1st grade there are 40 students,

$\frac{2}{5}$ of which are girls

How many girls are in the class?

❤️ Continue Your Math Journey!

We have hundreds of course questions with personalized recommendations + Account 100% premium

Step-by-step written solution

Follow each step carefully to understand the complete solution

Understand the problem

In 1st grade there are 40 students,

$\frac{2}{5}$ of which are girls

How many girls are in the class?

Step-by-step solution

To solve this problem, we will follow these steps:

Step 1: Identify the given information and apply the formula.
Step 2: Perform the necessary multiplication.

Let's begin:
Step 1: We know that there are 40 students in total, and $\frac{2}{5}$ of them are girls. According to the formula:
$\text{Number of girls} = 40 \times \frac{2}{5}$

Step 2: Perform the multiplication:
$\text{Number of girls} = 40 \times \frac{2}{5} = \frac{40 \times 2}{5} = \frac{80}{5}$

Dividing 80 by 5 gives us:
$\frac{80}{5} = 16$

Thus, the number of girls in the class is 16.

Therefore, the solution to the problem is $16$ .

Final Answer

Key Points to Remember

Essential concepts to master this topic

Rule: Multiply whole number by numerator, then divide by denominator
Technique: $40 \times \frac{2}{5} = \frac{40 \times 2}{5} = \frac{80}{5}$
Check: Verify 16 girls makes sense: 16 + 24 boys = 40 total ✓

Common Mistakes

Avoid these frequent errors

Adding the fraction to the whole number instead of multiplying
Don't add 40 + 2/5 = 40.4! This gives a meaningless answer because you can't have 40.4 students. Always multiply the whole number by the fraction to find the part of the total.

Practice Quiz

Test your knowledge with interactive questions

Fill in the missing sign:

$\frac{5}{25}☐\frac{1}{5}$

FAQ

Everything you need to know about this question

Why do I multiply instead of divide when finding a fraction of a number?

"Of" means multiply in math! When you see "2/5 of 40," it's asking for 2/5 × 40. Think of it as taking 2 parts out of every 5 parts of the 40 students.

Can I solve this a different way?

Yes! You can think of it as: First find 1/5 of 40 = 8 students, then multiply by 2 to get 2/5 of 40 = 16 students. Both methods give the same answer!

How do I know if 16 girls is reasonable?

Check if it makes sense: If 16 are girls, then 40 - 16 = 24 are boys. Since 16 < 24, there are more boys than girls, which matches 2/5 < 3/5.

What if the fraction doesn't divide evenly?

Sometimes you might get a decimal or mixed number! For example, $\frac{2}{5}$ of 41 would give 16.4, which you'd need to round appropriately since you can't have partial people.

Do I always multiply the whole number by the numerator first?

Yes! The order is: whole number × numerator, then ÷ denominator. This prevents errors and keeps your work organized. You can also think of it as $\frac{\text{whole} \times \text{numerator}}{\text{denominator}}$ .

🌟 Unlock Your Math Potential

Get unlimited access to all 18 Operations with Fractions questions, detailed video solutions, and personalized progress tracking.

📹

Unlimited Video Solutions

Step-by-step explanations for every problem

📊

Progress Analytics

Track your mastery across all topics

🚫

Ad-Free Learning

Focus on math without distractions

No credit card required • Cancel anytime