$A$ gaseous mixture contains $50\%$ helium and $50\%$ methane by volume. Find the percentage by weight of methane in this gaseous mixture.

If $\tan x + \tan \left(x + \frac{\pi}{3}\right) + \tan \left(x + \frac{2\pi}{3}\right) = 3$,then $\tan 3x$ is equal to

The density of gas $A$ is twice that of gas $B$. At the same temperature,the molecular weight of gas $B$ is twice that of gas $A$. The ratio of the pressure of gas $A$ to gas $B$ is:

$A$ tower,of $x$ metres high,has a flagstaff at its top. The tower and the flagstaff subtend equal angles at a point distant $y$ metres from the foot of the tower. Then,the length of the flagstaff (in metres) is:

$A$ $Ge$ specimen is doped with $Al$. The concentration of acceptor atoms is $\sim 10^{21} \text{ atoms}/m^3$. Given that the intrinsic concentration of electron-hole pairs is $\sim 10^{19} /m^3$,the concentration of electrons in the specimen is:

The solution of the differential equation $\frac{dy}{dx} = \frac{x-2y+1}{2x-4y}$ is