Rugby and ballet
What is the average weight of five ballet dancers and ten rugby players?
Age
11 to 14
Challenge level
Problem
The total mass of five rugby players is $425 \; \text{kg}$.
The average (mean) mass of ten ballet dancers is $40 \; \text{kg}$.
What is the average mass of all fifteen people?
Student Solutions
The mass of the $10$ ballet dancers is $$10 \times 40 \; \text{kg}= 400\; \text{kg} $$
The average mass of all $15$ people is $$\frac{425 \; \text{kg}+ 400 \; \text{kg}}{15}= \frac{825 \; \text{kg}}{15 }= 55\; \text{kg} $$