If the $p^{th}$,$q^{th}$,and $r^{th}$ terms of a harmonic progression are $u$,$v$,and $w$ respectively,then the value of $(q - r)vw + (r - p)wu + (p - q)uv$ is equal to:

If $x = \sum_{n=0}^{\infty} a^n$,$y = \sum_{n=0}^{\infty} b^n$,and $z = \sum_{n=0}^{\infty} c^n$,where $a, b, c$ are in arithmetic progression and $|a| < 1, |b| < 1, |c| < 1$,then $x, y, z$ are in which progression?

Let the positive numbers $a, b, c, d$ be in $A.P.$,then $abc, abd, acd, bcd$ are

If $\frac{x + y}{2}, y, \frac{y + z}{2}$ are in $H.P.$,then $x, y, z$ are in

An automobile driver travels from a plane to a hill station $120 \ km$ distant at an average speed of $30 \ km/hr$. He then makes the return trip at an average speed of $25 \ km/hr$. He covers another $120 \ km$ distance on the plane at an average speed of $50 \ km/hr$. His average speed over the entire distance of $360 \ km$ will be:

If $a, b, c$ are in $H.P.$,then which one of the following is true?