Motorboat covers a certain distance downstream in a river in 20 hours....
GIVEN:
Time taken for Downstream = 20 hours
Time taken for Upstream = 30 hours
Speed of water = 12 km/hr
FORMULA USED:
Downstream speed = speed of boat + speed of water
Upstream speed = speed of boat – speed of water
Speed = Distance/Time
CALCULATION:
Let the distance be ‘D’ km
speed of boat = x km/hour
speed of water = y km/hour
According to the question,
Downstream speed
x + y = d/20 or d = 20 (x + y) ----(i)
Upstream speed
x – y = d/30 or d = 30(x – y) ----(ii)
Comparing (i) & (ii)
20(x + y) = 30(x – y)
2(x + y) = 3(x – y)
2x + 2y = 3x – 3y
x = 5y
Hence, y = Speed of the current = 12 km/hour.
Speed of boat, x = 5 × 12
= 60 km/hour