Boatman covers $d$ km against current in $p$ hr, along current in $q$ hr. Speed of boat = ?

Question

Accepted Answer

$\dfrac{d}{2}\left(\dfrac{1}{p} + \dfrac{1}{q}\right)$

Answer

$\dfrac{d}{2}\left(\dfrac{1}{p} - \dfrac{1}{q}\right)$

Answer

$\dfrac{d}{2}\left(\dfrac{1}{q} - \dfrac{1}{p}\right)$

Answer

$d(p+q)$

Boatman covers ddd km against current in ppp hr, along current in qqq hr. Speed of boat = ?