Question
Your camera’s zoom lens has an adjustable focal length ranging from 80.0 to 200 mm. What is its range of powers?

$5\textrm{ D} \leq P \leq 12.5 \textrm{ D}$

OpenStax College Physics for AP® Courses, Chapter 25, Problem 37 (Problems & Exercises)

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Video Transcript
This is College Physics Answers with Shaun Dychko. Power of a lens in dioptres is the reciprocal of the focal length written in meters and so the minimum power is going to be the reciprocal of the maximum focal length and we are told that it's 200 millimeters and we write 200 times ten to the minus three meters in that denominator here and this gives a power of five dioptres and for the maximum power, we'll take reciprocal of the minimum focal length which is 80 millimetres and that is 12.5 dioptres and so the powers greater than or equal to five dioptres but less than or equal to 12.5.