What causes the formation of beats in sounds?

$41$ tuning forks are arranged in increasing order of frequency. Each tuning fork produces $5 \, \text{beats/sec}$ with the next one. If the frequency of the last tuning fork is double that of the first, what are the frequencies of the first and last tuning forks?

Two vibrating tuning forks produce progressive waves given by ${y_1} = 4\,\sin \left( {500\pi t} \right)$ and ${y_2} = 2\,\sin \left( {506\pi t} \right)$. These tuning forks are held near the ear of a person. The person will hear $\alpha \, \text{beats/s}$ with intensity ratio between maxima and minima equal to $\beta$. Find the value of $\beta - \alpha$.

If two waves of the same amplitude,having frequencies $340 \ Hz$ and $335 \ Hz$,are moving in the same direction,then the time interval between two successive maxima formed (in seconds) is:

Two vibrating tuning forks produce progressive waves given by $y_1 = 4 \sin(500 \pi t)$ and $y_2 = 2 \sin(506 \pi t)$. These tuning forks are held near the ear of a person. The person will hear

Each of the two strings of length $51.6 \, cm$ and $49.1 \, cm$ are tensioned separately by $20 \, N$ force. The mass per unit length of both strings is the same and equal to $1 \, g/m$. When both strings vibrate simultaneously,the number of beats is: