\textbf{187.} A simple pendulum oscillates at a fixed location with a period of 2 seconds and completes N full oscillations in 2.6 minutes. By what percentage should we decrease or increase the length of the pendulum so that in the same time duration and at the same location, $18 - N$ full oscillations are completed?
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(1) 69\% decrease \quad (2) 69\% increase \quad (3) 31\% decrease \quad (4) 31\% increase
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