If the $p^{th}$ term of a harmonic progression is $qr$ and the $q^{th}$ term is $pr$,then what is its $r^{th}$ term?

An aeroplane flies around a square,the sides of which measure $100$ miles each. The aeroplane covers the first side at a speed of $100 \text{ mph}$,the second side at $200 \text{ mph}$,the third side at $300 \text{ mph}$,and the fourth side at $400 \text{ mph}$. The average speed of the aeroplane around the square is ....... $\text{mph}$.

The harmonic mean of $3, 7, 8, 10, 14$ is

If $\log (x + z) + \log (x + z - 2y) = 2\log (x - z),$ then $x, y, z$ are in

If $\tan B = \frac{2 \sin A \sin C}{\sin (A+C)}$,then $\tan A, \tan B$ and $\tan C$ are in

If $H$ is the harmonic mean between $a$ and $b$,then what is the value of $\frac{1}{H - a} + \frac{1}{H - b}$?