Answer: 8 kmph

Explanation:
Let the speed of the boat in still water be x kmph.
=> Speed downstream = (x + 4) kmph, Speed upstream = (x – 4) kmph
=> Time taken to go 6 km downstream = 6/(x -4), time taken to go
=> 6 km upstream = 6/(x – 4) * 6/(x +4) + 6/ (x – 4) = 2 hours.
Solving the equations x = 8

Answer: 2.5 kmph

Explanation:
Speed of the stream = ½ (13 – 8) kmph = 2.5 kmph

Answer: 12

Explanation:
Speed of the boat in still water = 20/2 = 10 kmph
=> Let the total distance covered be 2x km
=> Given that, x/10+6 + x/10-6 = 3.75
x = 12

Answer: 5

Explanation:
Speed of Anand’s boat downstream = 8 kmph
Time taken = 40/8 = 5 hours.

Answer: 2 km 275 m

Explanation:
Man’s rate downstream = (5 + 1.5) kmph = 6.5 kmph
=> Man’s rate upstream = (5 – 1.5) kmph = 3.5 kmph
=> Let the distance be x km
=> Total time taken to row x km and back
=> = (x / 6.5 + x / 3.5) = 1
=> x = 2.275 km
thus the distance = 2 km 275 m

Answer: 8 kmph

Explanation:
Speed in still water = ½ (11 + 5) = 8 kmph

Answer: 14

Explanation:
Let the speed of the boat in still water be x kmph.
=> X+6 / x-6 = 5/2
=> 2x + 12 = 5x – 30
x = 14

Answer: 6 kmph

Explanation:
Rate downstream = 16/2 kmph = 8 kmph ; Rate upstream = 16/4 kmph = 4 kmph
Hence, Speed in still water = ½ (8 + 4) kmph = 6 kmph

Answer: 2 kmph

Explanation:
Let the speed upstream and speed downstream be Su and Sd respectively
=> Su = (1000/30)(1/60) = 5/9 m/s
=> Sd = (1000/10) (1/60) = 5/3 m/s
=> Let the speed of the boat and the current be x m/s and y m/s respectively
=> x + y = 5/3
=> x – y = 5/9
=> Solving these two equations simultaneously,
=> y = 5/9 m/s = 5/9 (3600 / 1000) = 2 kmph
The speed of the current = 2 kmph

Answer: 1 hr 15 mins

Explanation:
Rate downstream = (1/10 * 60) kmph = 6 kmph, Rate Upstream = 2 kmph
Speed in still water = ½ (6 + 2) kmph = 4 kmph
Hence, Required time = 5/4 hrs = 1 ¼ hours = 1 hr 15 mins