Solution to 2008 Problem 15

Lenses (A) and (B) are diverging, hence they have negative focal lengths. Lens (C), (D), and (E) are all converging, hence they have positive focal lengths. Lens (C) is curved on only one side, and the curvature on that side is less than the curvature of either side of lens (D) or (E), so lens (C) will have a larger focal length than (D) or (E). Lens (E) has larger curvature than lens (D), so it will have the shorter focal length. Hence answer (E) is correct.

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