Author note — to cover

C equals pi d or 2 pi r — G17 names these among formulae to know — deciding first whether the given length is a radius or a diameter, rounding sensibly, and reversing to find d or r from a given circumference. Exact-pi answers and part circles are sibling pages. Both tiers. (G17)

• Fluency — direct questions on circumference of a circle, 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).