Three sound waves of equal amplitudes have frequencies $(\nu -1)$, $\nu$, $(\nu +1)$. They superpose to give beats. The number of beats produced per second will be:

Beats are produced by the difference in frequencies. When multiple frequencies are present, the beat frequency is generally determined by the difference between the highest and lowest frequencies present in the group.Here, ${\nu }_{max}=\nu +1$ and ${\nu }_{min}=\nu -1$.Beat frequency $=(\nu +1)-(\nu -1)=2$.