Two tuning forks A and B give 4 beats per second. The frequency of A is 256 Hz. On loading B slightly, we get 5 beats in 2seconds. The frequency of B after loading is

nA = Known frequency = 256 Hz, nB = ?x = 4 beats per sec which is decreasing (4 bps to 52 bps) after loading (i.e. x↓)Unknown tuning fork B, is loaded so nB↓Hence  nA – nB↓  = x↓        ... (i)        →        Wrong           nB↓  – nA = x↓        ... (ii)         →      Correct ⇒ nB = nA + x = 256 + 4 = 260 Hz.