When two waves of almost equal frequencies $n_1$ and $n_2$ reach a point simultaneously,what is the time interval between successive maxima?

Two sound waves travelling in the same direction have displacements $y_1 = a \sin(0.2 \pi x - 50 \pi t)$ and $y_2 = a \sin(0.15 \pi x - 46 \pi t)$. How many times can a listener hear sound of maximum intensity in one second?

Beats are the result of

Two sources of sound are emitting progressive waves $y_1 = 4 \sin(710 \pi t)$ and $y_2 = 3 \sin(702 \pi t)$. The sources are placed close to each other. The number of beats heard per second and the intensity ratio between waxing and waning are respectively:

Two waves $y_1 = 0.35 \sin(316 t)$ and $y_2 = 0.35 \sin(310 t)$ are propagating along the same direction. The number of beats produced per second is:

In a guitar,two strings $A$ and $B$ made of the same material are slightly out of tune and produce beats of frequency $6 \, Hz$. When the tension in $B$ is slightly decreased,the beat frequency increases to $7 \, Hz$. If the frequency of $A$ is $530 \, Hz$,the original frequency of $B$ will be $......... \, Hz$.