Question: 11 -

The speed at which a man can row a boat in still water is 15 kmph. If he rows downstream, where the speed of current is 3 kmph, what time will he take to cover 60 metres? 

15 seconds

20 seconds

12 seconds

10 seconds

Answer:

12 seconds

Solution:

Speed of the boat downstream = 15 + 3 = 18 kmph
= 18 * 5/18 = 5 m/s
Hence time taken to cover 60 m = 60/5 = 12 seconds.

Question: 12 -

A man can row at 5 km/hr in still water, if the river is running at 1 km/hr it takes him 75 minutes to row to a place and back. How far is the place? 

5 km

3km

2.5km

4 km

Answer:

3km

Solution:

Speed downstream = (5+1)km/hr = 6 km/hr 

Speed upstream = (5-1)km/hr = 4 km/hr 

Let the required distance be x km. 

Then x/6 + x/4 = 75/60 = 5/4 => (2x + 3x) =15 => x =3. 

Required distance = 3 km 

Question: 13 -

A boat is rowed downstream at 15.5km/hr and upstream at 8.5 km/hr. The speed of the stream is? 

6.5km/hr

7km/hr

5.75km/hr

3.5km/hr

Answer:

3.5km/hr

Solution:

Speed Downstream = 15.5 km/hr, 

speed upstream = 8.5 km/hr 

Speed of the stream = ½ (15.5 “ 8.5)km = 3.5 km/hr 

Question: 14 -

A man can row downstream at 18 kmph and upstream at 10 kmph. Find the speed of the man in still water and the speed of stream respectively? 

14, 4

12, 6

15, 3

13, 3

Answer:

14, 4

Solution:

Let the speed of the man in still water and speed of stream be x kmph and y kmph respectively.
Given x + y = 18 --- (1) 
and x - y = 10 --- (2)
From (1) & (2) 2x = 28 => x = 14, y = 4.

Question: 15 -

A boat running downstream covers 24 km's in 4 hours while for covering the same distance upstream it takes 6 hours whats the speed of the boat in still water? 

Data Inadequate

3.5km/hr

None of these

5.5 km/hr

Answer:

None of these

Solution:

Speed downstream = 24/4 km/hr = 6 km/hr 

Speed upstream = 24/6 km/hr = 4 km/hr 

Speed of the boat in still water = ½ (6 +4)km/hr = 5 km/hr