Answer:
(c) 3 km
Explanation:
Speed in still water: 8 km/h
Speed of river: 2 km/h
Speed downstream: 8 km/h + 2 km/y = 10 km/h
Speed upstream: 8 km/h - 2 km/h = 6 km/h
total time both ways: 48 minutes = 48/60 hour = 0.8 hour
time to go upstream: t
time to go downstream: 0.8 - t
speed = distance/time
s = d/t
d = st
Upstream:
d = st
d = 6t
Downstream:
d = st
d = 10(0.8 - t)
The distance upstream and downstream is the same.
6t = 10(0.8 - t)
6t = 8 - 10t
16t = 8
t = 0.5
d = 6t = 6(0.5)
d = 3
Answer: (c) 3 km