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