Question

A person can row 18 km downstream and 12 km upstream in 3 hrs also he can row 36 km downstream and 40 km upstream in 8hrs find the distance of person in still water and the speed of water current

Answer 1

Speed of boat= 10km/hr
speed of stream=2 km/hr

Answer 2

Hey,

LET THE SPEED OF THE boat in still water = x km/hr
downstream:
distance travelled= 18 km
time taken = 3 hrs
speed = 18/3
          =6 km/hr
speed of stream= (6-x) km/hr (1)

UPSTREAM:
distance = 12 km
time = 3 hrs
speed = 12/3=4 km/hr
speed of stream =(x-4) km/hr   (2)

as speed of stream is constant:
(1)=(2)
(6-x) = (x-4)
6-x = x-4
6+4 = x+x
10 = 2x
5 = x

therefore, speed of boat in still water  = 5 km/hr
speed of water current = 1 km/hr

HOPE IT HELPS YOU:-))