UPSC 2015 CDS I Math Paper

Suppose A overtakes B after t hours.
Distance covered by A in t hours =p×t
Distance covered by B in t hours=q×t
Distance covered by A in t hours = c + Distance covered by B in t hours
∴ pt = c + qt
⇒ (p-q)t - c
⇒t=

c

p−q

Therefore, distance covered by A before he overtakes B=p×

c

p−q

=

pc

p−q

km