A tuning fork of known frequency 256 Hz makes 5 beats per second with the vibrating string of piano when tension in the wire of piano increased by 2% then beat frequency decreases by 2 beats per seconds, the frequency of piano string before increase in tension will be
as it is producing 5 beats per sec probable frequency of piano could be 261 or 251 Hz. now increase in tension frequency increases and beat frequency decreases i.e it must be 251 and increases to 253