\textbf{193-} Air inside a closed tube, open at both ends, forms 3 nodes in the tube. In this case, if the sequential distance of 2 nodes is $25\ \text{cm}$, what is the fundamental frequency of the tube? (Speed of sound in air inside the tube is $340\ \dfrac{\text{m}}{\text{s}}$.)
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(1) $170$ \hfill (2) $340$ \hfill (3) $510$ \hfill (4) $680$
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