UPSC 2017 CDS II Math Paper

Let the speed of the man rowing in still water be x km/hr and the speed of the stream be y km/hr.
Speed of the man against the stream = (x - y) km/hr
Speed of the man with the stream = (x + y) km/hr
Distance covered by the man = 18 km
∴(x−y)×10=18
⇒x−y=1.8km/hr....(1)
Hence, statement 1 is correct.
(x+y)×4=18
⇒x+y=4.5km/hr....(2)
Adding (1) and (2), we get
2x=1.8+4.5=6.3
⇒x=3.15km/hr
Hence, statement 2 is correct.
Putting x=3.15 in (2) we get
y=4.5−3.15=1.35km/hr