Author note — to cover

Reverse mean problems on ungrouped data: recover the total as mean times count, find a missing value given the mean, and find the new mean after adding or removing one value. Include multi-step worded versions. Combining two groups through their totals is the sibling Combined means page. Both tiers. (S4)

• Fluency — direct questions on working backwards from the mean, limited to this lesson's stated scope (4 questions).
• Application — use the same skill in unfamiliar or contextual questions without introducing a later method (4 questions).
• Check — questions built around the exclusions and likely misconceptions named in the lesson brief (4 questions).