Finding the mean shares a total out; this runs it backward. These free printable worksheets give a set with one number missing and the mean the whole set should have, and ask what the missing number is — the question that shows whether "the mean is the total shared out" is really understood.
If they get stuck
The answer key prints on a separate page.
The step a child skips is the first one: a mean of 8 over five numbers means the five must add to 8 × 5 = 40. Once the total is in hand, the missing number is just what is left after the ones you were given — 40 minus their sum. Every step-by-step walk multiplies the mean up before it subtracts, because that multiplication is the whole idea.
It is the exact inverse of the mean sheets, and doing both is what turns the mean from a recipe into a thing a child can reason about — forward to summarize a set, backward to hit a target. A test average that needs a certain last score is the same question a student meets for real.
One question from a sheet like this one, worked a step at a time — with a sentence saying what just happened and why.
Missing number from the mean, step by step