A motor boat takes 12 hours to go downstream and it takes 24 hours to return the same distance. what is the time taken by boat in still water?

Correct Answer: 180 km

Explanation:

Speed in downstream = (14 + 4) km/hr = 18 km/hr;

Speed in upstream = (14 ? 4) km/hr = 10 km/hr.

Let the distance between A and B be x km. Then,

x/18 + (x/2)/10 = 19 ? x/18 + x/20 = 19 ? x = 180 km.

Correct Answer: 9 km/hr, 3 km/hr

Explanation:

Let the speed of the boat = p kmph

Let the speed of the river flow = q kmph

From the given data,

2 x 28 p + q = 28 p - q

 

=> 56p - 56q -28p - 28q = 0

=> 28p = 84q

=> p = 3q.

Now, given that if

$$\begin{gathered} 28 3 q + 2 q + 28 3 q - 2 q = 672 60 \\ = > 28 5 q + 28 q = 672 60 \\ = > q = 3 kmph \\ = > x = 3 q = 9 kmph \end{gathered}$$

 

Hence, the speed of the boat = p kmph = 9 kmph and the speed of the river flow = q kmph = 3 kmph.

Correct Answer: 4 2⁄3 Kmph

Explanation:

Let man’s rate upstream be x km/hr. Then his rate downstream is 3 x km/hr Given: Speed in still water = 9 (1/3) = 28/3 km/hr i.e, ½ (a+b) = 28/3 km/hr ½ (x+3x) = 28/3 2x = 28/3 x = 28/ 2 x 3 = 14/3 km/hr rate upstream b = 14/3 km/hr and rate downstream a = 14/3 x 3 = 14 km/hr speed of the current = ½ (a-b) = ½ (14 – 14/3) = ½ (42-14/3) = 28/6 = 4 (2/3) km/hr

Correct Answer: 3h

Explanation:

Upstream speed = B-S

Downstream speed = B+s

B-S = 15/5 = 3 km/h

Again          B= 4S

Therefore    B-S = 3= 3S

=>             S = 1 and B= 4 km/h

Therefore    B+S = 5km/h

Therefore, Time during downstream = 15/5 = 3h

Correct Answer: (x+y-xy100)%

Correct Answer: 6 kmph

Explanation:

Speed of the stream = 1
Motor boat speed in still water be = x kmph
Down Stream = x + 1 kmph
Up Stream = x - 1 kmph
[35/(x + 1)] + [35/(x - 1)] = 12
x = 6 kmph

Correct Answer: 1.5 kmph

Explanation:

Speed of Boy is B = 4.5 kmph

Let the speed of the stream is S = x kmph

Then speed in Down Stream = 4.5 + x

speed in Up Stream = 4.5 - x

As the distance is same,

=> 4.5 + x = (4.5 - x)2

=> 4.5 + x = 9 -2x

3x = 4.5

x = 1.5 kmph

Correct Answer: 21 km

Explanation:

Let the distance covered be D km. 

  D 10 + 4 + D 10 - 4 = 5

  D 14 + D 6 = 5

 10D = 42 x 5 = 210

 

=> D = 21 km

Correct Answer: 5 kmph

Explanation:

Speed of the boat downstream  s=a/t= 60/3 = 20 kmph

Speed of the boat upstream s= d/t = 30/3= 10 kmph

 

Therefore,  The speed of the stream =  s p e e d o f d o w n s t r e a m - s p e e d o f u p s t r e a m 2=5 kmph

Correct Answer: 1/2 kmph

Explanation:

Speed in upstream = Distance / Time = 3 x 60/20 = 9 km/hr.

Speed in downstream = 3 x 60/18 = 10 km/hr

Rate of current = (10-9)/2 = 1/2 km/hr.