A boat can travel 20 km downstream in 24 min. The ratio of the speed o...
Down speed = 20/24*60 = 50km/hr
4:1 = 4x:x
Downstream speed = 4x+x = 5x
Upstream speed = 4x-x = 3x
5x = 50; x = 10
so up speed 3*10 = 30
Time = 15/30*60 = 30min.
View all questions of this testA boat can travel 20 km downstream in 24 min. The ratio of the speed o...
Down speed = 20/24*60 = 50km/hr
4:1 = 4x:x
Downstream speed = 4x+x = 5x
Upstream speed = 4x-x = 3x
5x = 50; x = 10
so up speed 3*10 = 30
Time = 15/30*60 = 30min.
A boat can travel 20 km downstream in 24 min. The ratio of the speed o...
Given:
Speed ratio of the boat in still water to the speed of the stream = 4:1
Let the speed of the boat in still water be 4x and the speed of the stream be x.
Speed of the boat downstream = (4x + x) km/hr = 5x km/hr
Distance travelled downstream in 24 min = 20 km
Speed = Distance/Time
Time taken to travel 20 km downstream = 24 min = 24/60 hours = 2/5 hours
Therefore, 5x = 20/(2/5) = 50 km/hr
Speed of the boat upstream = (4x - x) km/hr = 3x km/hr
Time taken to travel 15 km upstream = Distance/Speed
= 15/3x
= 5/x hours
= (5/x) * 60 minutes
= 300/x minutes
Substituting x = 10 km/hr, we get
Time taken to travel 15 km upstream = 300/10 minutes = 30 minutes = 0.5 hours
Therefore, the boat will take 30 minutes or 0.5 hours to cover 15 km upstream.
Hence, the correct answer is option D.