Calculate the Average Number of Siblings per Student in a 45-Strong Class

To solve this problem, we'll follow these steps:

• Step 1: Determine the number of students with no siblings.
• Step 2: Calculate the total number of siblings.
• Step 3: Use the weighted average formula to find the average number of siblings per student.

Step 1: Determine the number of students with no siblings.

The problem provides us with the following information:
- 20 students have 2 siblings.
- 15 students have 1 sibling.
- Total number of students = 45.

The number of students with no siblings can be calculated as:

Number of students with no siblings = Total number of students - Students with 2 siblings - Students with 1 sibling.

$45 - 20 - 15 = 10$

Step 2: Calculate the total number of siblings.

The total number of siblings is calculated by summing the product of the number of siblings and the number of students in each category:

Total number of siblings = (2 siblings × 20 students) + (1 sibling × 15 students) + (0 siblings × 10 students)

$(2 \times 20) + (1 \times 15) + (0 \times 10) = 40 + 15 + 0 = 55$

Step 3: Use the weighted average formula.

The weighted average for the number of siblings per student is given by:

Average number of siblings = $\frac{\text{Total number of siblings}}{\text{Total number of students}}$

$\frac{55}{45} = \frac{11}{9} \approx 1.22$

Therefore, the students in the class have, on average, $1.22$ siblings.