The speed of a stationary wave represented by the equation

$$ y=0.7 \sin \left(\frac{7 \pi}{4} x\right) \cos (350 \pi t) \text { is } $$

(In the given equation $x$ and $y$ are in metre and $t$ is in second)

Two sound waves of wavelengths 99 cm and 100 cm produce 10 beats in a time of $t$ seconds. If the speed of sound in air is $330 \mathrm{~ms}^{-1}$, then the value of $t$ in seconds is

The fundamental frequency of an open pipe is 100 hz If the bottom end of the pipe is closed and $1 / 3$ rd of the pipe is filled with water, then the fundamental frequency of the pipe is