This problem falls under the Percentages topic, which is often used in everyday applications to compare parts to a whole.

Problem:

"In a class, 60% of the students are girls. If the total number of students is 30, what is the number of boys?"

Solution:

1. Understand the Question:

   • Total students = $30$
   • Percentage of girls = $60\%$
   • We need to find the number of boys.

2. Find the Number of Girls: The number of girls is $60\%$ of $30$. To calculate: $\text{Number of girls} = \frac{60}{100} \times 30 = 18$

3. Find the Number of Boys: Since the total number of students is $30$, and there are $18$ girls: $\text{Number of boys} = 30 - 18 = 12$

Final Answer:

The number of boys is C. 12.

Would you like further clarification on this or practice on similar problems?

Relative Questions:

1. How do you calculate percentages of a given number?
2. What is the formula for finding a percentage decrease or increase?
3. Can you solve similar problems with different percentages and totals?
4. What are common real-life applications of percentages?
5. How do percentages relate to fractions and decimals?

Tip:

When solving percentage problems, always convert the percentage into a fraction or decimal before applying it to the total number.