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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?
An investigation involving adding and subtracting sets of consecutive numbers. Lots to find out, lots to explore.
Investigate how you can work out what day of the week your birthday will be on next year, and the year after...