Two identical flutes produce fundamental notes of frequency 300 Hz at $27^{\circ}C$. If the temperature of the air in one of the flutes is increased to $31^{\circ}C$, the number of beats heard per seconds will be :

Question

$\begin {array} {1 1} (1)\;3 & \quad (2)\;2 \\ (3)\;1 & \quad (4)\;4 \end {array}$