Two tuning forks have frequencies $380 \, Hz$ and $384 \, Hz$ respectively. When they are sounded together,they produce $4 \, beats$ per second. After hearing the maximum sound,how long will it take to hear the minimum sound?

When two tuning forks $A$ and $B$ are sounded together, $4$ beats per second are heard. The frequency of the fork $B$ is $384 \,Hz$. When one of the prongs of the fork $A$ is filed and sounded with $B$, the beat frequency increases. Then the frequency of the fork $A$ is: (in $\,Hz$)

Two tuning forks when sounded together produce $4$ beats/sec. The frequency of one fork is $256 \, Hz$. The number of beats heard increases when the fork of frequency $256 \, Hz$ is loaded with wax. The frequency of the other fork is (in $, Hz$)

Two tuning forks $A$ and $B$ produce notes of frequencies $258 \,Hz$ and $262 \,Hz$. An unknown note sounded with $A$ produces certain beats. When the same note is sounded with $B$, the beat frequency gets doubled. The unknown frequency is (in $\,Hz$)

Two waves $Y_1 = 0.25 \sin(316t)$ and $Y_2 = 0.25 \sin(310t)$ are propagating along the same direction. The number of beats produced per second is:

$A$ set of $20$ tuning forks is arranged in a series of increasing frequencies. If each fork gives $4 \; Hz$ beats with respect to the preceding fork and the frequency of the last fork is twice the frequency of the first,then the frequency of the last fork is $\dots \; Hz$.