In a class of 30 students, the average weight of boys is 20 kg and the average weight of the girls is 25 kg. The fraction of boys out of the total students of the class is :

Options

A. `4/5`
B. `5/6`
C. `3/4`
D. data insufficient

Answer

To solve the problem step by step, we need to find the fraction of boys in a class of 30 students, given the average weights of boys and girls.

### Step 1: Define Variables
Let:
- \( B \) = number of boys
- \( G \) = number of girls

### Step 2: Set Up the Total Students Equation
From the problem, we know that the total number of students is 30. Therefore, we can write the equation:
\[ B + G = 30 \]

### Step 3: Express the Total Weight of Boys and Girls
The total weight of boys can be expressed as:
\[ \text{Total weight of boys} = B \times 20 \]
The total weight of girls can be expressed as:
\[ \text{Total weight of girls} = G \times 25 \]

### Step 4: Set Up the Total Weight Equation
We need to find the total weight of all students. However, we do not have the average weight of all students combined. Therefore, we cannot directly calculate the total weight of the class.

### Step 5: Analyze the Information Given
We have two equations:
1. \( B + G = 30 \)
2. Total weight of boys and girls expressed in terms of \( B \) and \( G \).

### Step 6: Determine the Fraction of Boys
To find the fraction of boys, we need to know the value of \( B \). However, since we do not have enough information to determine the total weight or the average weight of all students, we cannot find the exact number of boys.

### Conclusion
Since we cannot determine the number of boys from the information provided, we conclude that the data is insufficient to find the fraction of boys out of the total students.

### Final Answer
The fraction of boys out of the total students is **data insufficient**.

---