averaging expressions

extending finding the mean of a set of numbers to this task:
averaging a set of expressions

involves: simplification and substitution, including subtracting negatives

students could be asked to create their own sets of expressions, with a decent mean

related tasks:

show that the mean of four consecutive even numbers is an integer

show that the mean of four consecutive odd numbers is also an integer

what happens for the mean of five consecutive (i) even numbers (ii) odd numbers?

etc.