The average weight of a class of 40 students is 30 and the average weight of a class of 20 students is 15. Find the average weight of both the combined classes :

Options

A. 20
B. 25
C. 17.5
D. 15

Answer

To find the average weight of both combined classes, we can follow these steps:

### Step 1: Calculate the total weight of each class.
- For the first class of 40 students with an average weight of 30:
\[ \text{Total weight of first class} = \text{Number of students} \times \text{Average weight} = 40 \times 30 = 1200 \]

- For the second class of 20 students with an average weight of 15:
\[ \text{Total weight of second class} = \text{Number of students} \times \text{Average weight} = 20 \times 15 = 300 \]

### Step 2: Calculate the combined total weight of both classes.
\[ \text{Combined total weight} = \text{Total weight of first class} + \text{Total weight of second class} = 1200 + 300 = 1500 \]

### Step 3: Calculate the total number of students in both classes.
\[ \text{Total number of students} = \text{Number of students in first class} + \text{Number of students in second class} = 40 + 20 = 60 \]

### Step 4: Calculate the average weight of the combined classes.
\[ \text{Average weight of combined classes} = \frac{\text{Combined total weight}}{\text{Total number of students}} = \frac{1500}{60} = 25 \]

### Final Answer:
The average weight of both combined classes is **25**.

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