Mahesh rows to the place 80 km away and back in 20 hours. He finds that he can row 8 km downstream in the same time as 4 km upstream. The speed of the boat in stillwater is

Correct Answer: 4.5 km/h and 0.5 km/h

Explanation:

Distance travelled by boat in upstream=24km

Time taken = 6 h

Speed of the boat in upstream = 24/6 = 4 km/h

And distance travelled by boat in downstream = 20 km

Time taken = 4h Speed of the boat in downstream = 20/4 km/h = 5 km/h

Now, speed of the boat in still water = 1/2 [ speed of the boat in upstream + speed of the boat in downstream] =1/2 [4 + 5] = 1/2 × 9 = 4.5 km/h

And speed of the current = 1?2 [speed of the boat in downstream ? speed of the boat in upstream] = 1/2 [5 ? 4] = 1/2 × 1 = 0.5 km/h

Correct Answer: 9

Correct Answer: 13 kmph

Explanation:

Given that, upstream distance = 7 kms

Upstream speed = 7/42 x 60 = 10 kms

Speed of the stream = 3 kmph

Let speed in still water = M kmph, then

Upstream speed = M - 3 = 10

=> M = 13 kmph.

Correct Answer: 9 kmph

Explanation:

Speed of boat in still water = 1/2 (12 + 6) = 9 kmph.

Correct Answer: 4 kmph

Explanation:

Let the speed of current = 'C' km/hr

 

Given the speed of boat in still water = 6 kmph

 

Let 'd' kms be the distance it covers.

 

According to the given data,

 

Boat takes thrice as much time in going the same distance against the current than going with the current

 

i.e,  d 8 - C = 3 × d 8 + C

 

$$\begin{gathered} ? 24 - 3 C = 8 + C \\ ? 4 C = 16 \\ ? C = 4 kmph \end{gathered}$$

 

Hence, the speed of the current C = 4 kmph.

Correct Answer: 50

Explanation:

let speed of boat= X, speed of stream= Y
Upstream speed= X-Y
Downstream speed= X+Y
Sum of upstream & downstream= (X-Y) +(X+Y)= 2X
So, 2X= 40
X= 20 km/hr
Speed of boat : speed of stream= 600+100 :100= 7:1
So speed of Stream= 20/7 km/hr
ATQ, D/( X-Y) + D/( X+Y) = 5
D/(120/7) + D/(160/7)= 5
D= 480×5/49= 48.97 km= 50 Km(approx)

Correct Answer: Any one pair of A and B, B and C or C and A is sufficient

Explanation:

Let distance between A & B = d km
Let speed in still water = x kmph
Let speed of current = y kmph

from the given data,
d/x = 2

From A) we get d
From B) we get d/x+y
From C) we get y

 

So, Any one pair of A and B, B and C or C and A is sufficient to give the answer i.e, the speed of upstream.

Correct Answer: 12 km

Explanation:

Speed of boat in still water = 9 km/hr

Speed of current = 3km/hr

Downstream speed = 9+3 = 12 km/hr

Upstream speed = 9-3 =6 km/hr

Let the distance between A to B be x km.

x/6 + x/12 = 3x + 2x = 36
3x = 36
x = 12 km

Correct Answer: 40

Correct Answer: 4 km/h

Explanation:

Speed of streamer = 4.5 km/hrSpeed of water = 1.5 km/hr

Downstream speed = 4.5+1.5 = 6 km/hr

Upstream speed = 4.5 -1.5 = 3 km/hr

Average Speed = (6 X 3) / 4.5 = 4km/hr