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

The vibrations of four air columns are shown below. The ratio of frequencies is