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A city replaced the streetlights on its main avenue with new fixtures that each draw less electricity than the old ones. After the replacement, however, the avenue's total monthly electricity use for street lighting was higher than before. Which of the following, if true, most helps to explain this result?
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Correct answer
D
Each new fixture uses less power than the old one it replaced, yet the avenue's total monthly electricity use for lighting went up. For that to happen, the number of fixtures must have grown enough to outweigh the saving on each one.
(D) says exactly this: the city installed far more of the new fixtures than there had been old ones, and the combined power drawn by that larger number of efficient lamps exceeded what the smaller number of old, less efficient lamps had drawn. A saving per fixture can still produce a higher total once you multiply by a much larger fixture count.
(A) only repeats the premise that each new fixture is more efficient, which is already given and only sharpens the puzzle rather than resolving it. (B) points to purchase and installation cost, a dollar figure, not the electricity use that the question asks about. (C) describes how busy the avenue is, a fact that holds equally before and after the switch, so it cannot explain a change between the two periods. (E) concerns how long the old, now-removed fixtures had been in service, which cannot account for a total measured under the new fixtures.
Only (D) reconciles a lower draw per fixture with a higher total draw.
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