2
Q:

A boat takes 19 hours for travelling downstream from point A to point B and coming back to a point C which is at midway between A and B. If the velocity of the stream is 4 kmph and the speed of the boat in still water is 14 kmph, what is the distance between A and B ? 

A) 180 km B) 160 km
C) 140 km D) 120 km

Answer:   A) 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.

Q:

A boat running upstream takes 8 hours 48 minutes to cover a certain distance, while it takes 4 hours to cover the same distance running downstream. What is the ratio between the speed of the boat and speed of the water current respectively?

A) 7:4 B) 11:4
C) 4:7 D) 8:3
 
Answer & Explanation Answer: D) 8:3

Explanation:

Let the speed of the boat upstream be p kmph and that of downstream be q kmph

Time for upstream = 8 hrs 48 min =  hrs

Time for downstream = 4 hrs

Distance in both the cases is same.

=> p x  = q x 4

=> 44p/5 = 4q

=> q = 11p/5

 Now, the required ratio of Speed of boat : Speed of water current

=> (11p/5 + p)/2  : (11p/5 - p)/2

=> 8 : 3

Report Error

View Answer Workspace Report Error Discuss

6 71
Q:

In one hour, a boat goes 12 km/hr along the stream and 6 km/hr against the stream. The speed of the boat in still water (in km/hr) is:

A) 9 B) 8
C) 7 D) 7.5
 
Answer & Explanation Answer: A) 9

Explanation:

Speed in still water = Average of Speed in Upstream and speed in Downstream

= 1/2 (12 + 6) kmph = 9 kmph.

Report Error

View Answer Workspace Report Error Discuss

6 37
Q:

A motorboat running upstream takes 8 hours 48 minutes to cover a certain distance, while it takes 4 hours to cover the same distance running downstream. What is the ratio between the speed of the motorboat and speed of the water current respectively?

A) 3:7 B) 7:9
C) 5:4 D) 8:3
 
Answer & Explanation Answer: D) 8:3

Explanation:

Let the man's rate upstream be x kmph and that downstream be y kmph.

Then, distance covered upstream in 8 hrs 48 min = Distance covered downstream in 4 hrs.

x x 8 4 = (y x 4)
5
44 x =4y
5
 y = 11 x.
5
 Required ratio = y + x : y - x
2 2
   = 16x x 1 : 6x x 1
5 2 5 2
   = 8 : 3
5 5

   = 8 : 3.

Report Error

View Answer Workspace Report Error Discuss

7 33
Q:

A man can row upstream at 16 km/hr and downstream at 24 km/hr. Find the speed of the current.

A) 4 kmph B) 6 kmph
C) 5 kmph D) 3 kmph
 
Answer & Explanation Answer: A) 4 kmph

Explanation:

Speed of the current = 24-16/2

= 8/2

= 4 km/hr.

Report Error

View Answer Workspace Report Error Discuss

6 55
Q:

A motorboat can go 10 miles downstream on a river in 20 min. It takes 30 min for this boat to go back at the same 10 miles. Find the speed of the current ?

A) 8 m/h B) 5 m/h
C) 7 m/h D) 6 m/h
 
Answer & Explanation Answer: B) 5 m/h

Explanation:

As the distance travelled is constant, the time taken is inversely proportional to speed.

Let 'u' be the speed of the current and 'v' be the speed of the boat.

Speed of the boat downstream = v + u & upstream = v - u

=> v+u/v-u = 30/20 => v/u = 5 => v = 5u

=> v + u = 6u = 10/20/60 miles/hr

=> 6u = 30 m/h

=> u = 5 m/h

Report Error

View Answer Workspace Report Error Discuss

9 211