Answer:
The speed in still water is 12 km/h.
The upstream distance is 20 km.
Explanation:
speed of boat in still water = s
speed of current = 3 km/h
speed of boat upstream = s - 3
speed of boat downstream = s + 3
distance upstream = d
distance downstream = d + 2
time upstream = 2 hours
time downstream = 1 h 20 m = 1 1/3 h = 4/3 h
speed = distance/time
distance = speed × time
Upstream:
distance = speed × time
d = (s - 3) × (2)
d = 2s - 6 Eq. 1
Downstream:
distance = speed × time
d + 2 = (s + 3) × (4/3)
3d + 6 = 4s + 12
3d - 4s = 6 Eq. 2
Equations 1 and 2 form a system of equations:
d = 2s - 6
3d - 4s = 6
3(2s - 6) - 4s = 6
6s - 18 - 4s = 6
2s = 24
s = 12
d + 2 = (s + 3)(4/3) = (15)(4/3) = 20
The speed in still water is 12 km/h.
The upstream distance is 20 km.