MindTree Boats and Streams Quiz 1

Let x be the speed of man in still water and y be the speed of stream.

∴ Speed of man (x) = 60 km/hr and speed of downstream = 75 km/hr.

∴ Speed of stream = 15 km/hr.

Hence upstream speed = 60 – 15 = 45 km/hr.

So time taken to cover 20 km = 20/45*60 = 26.67min.

4 km downstream is covered in 15 min.
∴ speed of downstream = 16 km/hr.
So speed of upstream = 8km/hr.
Total time taken for downstream journey = 15 min (given).
Now total time taken for upstream journey = 8/8 = 1 hr = 60 min.
Hence total time taken from A to B = 15 + 60 = 75 min.
As average speed = Total distance /total time, so average speed from A to B = (12/75)*60 = 48/5 = 9.6kmph.

Speed of boat in still water = x = 5 km/hr.
Let rate of flow of river = y km/hr.
∴ Speed of u/s = 5- y and speed of d / s = 5 + y
∴ 90/(5+y) + 90/(5-y) = 100 ⇒ y = 4 km/hr.

Speed of upstream = 30 / 6 = 5 km / hr.
Speed of man in still water = 6 km / hr.
∴ Speed of current = 6 - 5 = 1 km / hr.
So speed of downstream = 6 + 1 = 7 km / hr.
∴ Distance traveled in 7 hrs = 10 * 7 = 70 km.

Let x be the speed of man in still water and y be the speed of current.
Speed of d / s = (2 / 10) × 60 = 12 km / hr. Speed of u / s = (2 / 20) × 60 = 6 km / hr.
∴ rate of current = (12 - 6) / 2 = 3 km/hr.

Let the distance between A and B be x km.
Speed downstream = 6 kmph, speed upstream = 2 kmph.
(x/6) + (x/2) = 4             ⇒ 4x = 24
∴ x = 6

Distance AB = 6 km.

Speed in still water = (1/2) * (6 + 2) km/hr = 4 km/hr

Speed downstream (10+6) km/hr 16 km/hr.
Time taken to cover 80 km downstream = (80/16) hrs = 5 hrs

Speed downstream = (15 + 3) kmph = 18 kmph.
Distance travelled = 18 x 12 / 60 km = 3.6 km

Let speed downstream = x kmph
Then Speed upstream = 2x kmph
So ratio will be,
(2x+x)/2 : (2x-x)/2
⇒ 3x/2 : x/2         ⇒ 3:1