Two strings X and Y of a sitar produce a beat frequency 4 Hz. When the tension of the string Y is slightly increased the beat frequency is found to be 2 Hz. If the frequency of X is 300 Hz, then the original frequency of Y was

nx=300Hz,  ny=?x = beat frequency = 4 Hz, which is decreasing (4→2)after increasing the tension of the string y. Also  tension of wire y increasing so ny​↑  (∵ n∝T)Hence nx−ny​↓=x​↓        →      Correct              ny​↑−nx=x​↓       →        Wrong ⇒ny=nx−x=300−4=296Hz