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Aptitude Boats And Streams Practice Q&A-Easy Page: 2
2437.A boat running downstream covers a distance of 16 km in 2 hours while for covering the same distance upstream, it takes 4 hours. What is the speed of the boat in still water?
4 km/hr
6 km/hr
8 km/hr
Data inadequate
Explanation:
Rate downstream =$ \left(\dfrac{16}{2} \right) $kmph = 8 kmph.
Rate upstream =$ \left(\dfrac{16}{4} \right) $kmph = 4 kmph.
$\therefore$ Speed in still water =$ \dfrac{1}{2} $(8 + 4) kmph = 6 kmph.
2438.A boat takes 90 minutes less to travel 36 miles downstream than to travel the same distance upstream. If the speed of the boat in still water is 10 mph, the speed of the stream is:
2 mph
2.5 mph
3 mph
4 mph
Explanation:

Let the speed of the stream $ x $ mph. Then,

Speed downstream = 10 + $ x $ mph,

Speed upstream = 10 - $ x $ mph.

$\therefore \dfrac{36}{(10 - x)} $-$ \dfrac{36}{(10 + x)} $=$ \dfrac{90}{60} $

$\Rightarrow$ 72$ x $ x 60 = $90 \left(100 - x^2\right)$

$\Rightarrow$ $ x $2 + 48$ x $ - 100 = 0

$\Rightarrow$ $ x + 50\left( x - 2\right)$ = 0

$\Rightarrow$ $ x $ = 2 mph.

2439.A Cistern is filled by pipe A in 8 hrs and the full Cistern can be leaked out by an exhaust pipe B in 12 hrs. If both the pipes are opened in what time the Cistern is full?
12 hrs
24 hrs
16 hrs
32 hrs
Explanation:

Pipe A can fill $\dfrac{1}{8}$ of the cistern in 1 hour.

Pipe B can empty $\dfrac{1}{12}$ of the cistern in 1 hour

Both Pipe A and B together can effectively fill $\dfrac{1}{8}-\dfrac{1}{12}=\dfrac{1}{24}$ of the cistern in 1 hour

i.e, the cistern will be full in 24 hrs.

2441.A boat covers a certain distance downstream in 1 hour, while it comes back in 1$ \dfrac{1}{2} $ hours. If the speed of the stream be 3 kmph, what is the speed of the boat in still water?
12 kmph
13 kmph
14 kmph
15 kmph
Explanation:

Let the speed of the boat in still water be $ $ kmph. Then,

Speed downstream = $ x $ + 3 kmph.

Speed upstream = $ x $ - 3 kmph.

$\therefore$ $ x $ + 3 x 1 = $ x $ - 3 x $ \dfrac{3}{2} $

$\Rightarrow$ 2$ x $ + 6 = 3$ x $ - 9

$\Rightarrow x $ = 15 kmph.

2442.A man takes twice as long to row a distance against the stream as to row the same distance in favour of the stream. The ratio of the speed of the boat in still water and the stream is:
2 : 1
3 : 1
3 : 2
4 : 3
Explanation:

Let mans rate upstream be $ x $ kmph.

Then, his rate downstream = 2$ x $ kmph.

$\therefore$ Speed in still water : Speed of stream =$ \left(\dfrac{2x + x}{2} \right) $:$ \left(\dfrac{2x - x}{2} \right) $
   =$ \dfrac{3x}{2} $:$ \dfrac{x}{2} $

   = 3 : 1.

2443.Two pipes A and B can fill a tank in 10 hrs and 40 hrs respectively. If both the pipes are opened simultaneously, how much time will be taken to fill the tank?
8 hours
6 hours
4 hours
2 hours
Explanation:

Pipe A can fill $\dfrac{1}{10}$ of the tank in 1 hr

Pipe B can fill $\dfrac{1}{40}$ of the tank in 1 hr

Pipe A and B together can fill $\dfrac{1}{10}+\dfrac{1}{40}=\dfrac{1}{8}$ of the tank in 1 hr

i.e., Pipe A and B together can fill the tank in 8 hours

2444.A boat can travel with a speed of 12 km/hr in still water. If the speed of the stream is 4 km/hr, find the time taken by the boat to go 68 km downstream.
4 hr
4.25 hr
4.5 hr
6 hr
Explanation:

speed of boat in still water = 12 km/hr

speed of the stream = 4 km/hr

Speed downstream = (12+4) = 16 km/hr

Time taken to travel 68 km downstream $=\dfrac{68}{16}=\dfrac{17}{4}$ = 4.25 hours

2452.A boat can travel with a speed of 22 km/hr in still water. If the speed of the stream is 5 km/hr, find the time taken by the boat to go 54 km downstream
5 hours
4 hours
3 hours
2 hours
Explanation:

Speed of the boat in still water = 22 km/hr

speed of the stream = 5 km/hr

Speed downstream = (22+5) = 27 km/hr

Distance travelled downstream = 54 km

Time taken $=\dfrac{\text{distance}}{\text{speed}} = \dfrac{54}{27}\text{ = 2 hours}$

2453.A boat running downstream covers a distance of 22 km in 4 hours while for covering the same distance upstream, it takes 5 hours. What is the speed of the boat in still water?
5 kmph
4.95 kmph
4.75 kmph
4.65 kmph
Explanation:

Speed downstream $=\dfrac{22}{4}\text{ = 5.5 kmph}$

Speed upstream $=\dfrac{22}{5}\text{ = 4.4 kmph}$

Speed of the boat in still water $=\dfrac{5.5+4.4}{2}\text{ = 4.95 kmph}$

2456.Speed of a boat in standing water is 9 kmph and the speed of the stream is 1.5 kmph. A man rows to a place at a distance of 105 km and comes back to the starting point. The total time taken by him is:
16 hours
18 hours
20 hours
24 hours
Explanation:

Speed upstream = 7.5 kmph.

Speed downstream = 10.5 kmph.

$\therefore$ Total time taken =$ \left(\dfrac{105}{7.5} +\dfrac{105}{10.5} \right) $hours = 24 hours.
2457.In one hour, a boat goes 11 km/hr along the stream and 5 km/hr against the stream. The speed of the boat in still water in km/hr is:
3 km/hr
5 km/hr
8 km/hr
9 km/hr
Explanation:
Speed in still water =$ \dfrac{1}{2} $(11 + 5) kmph = 8 kmph.
2459.A boat can travel with a speed of 13 km/hr in still water. If the speed of the stream is 4 km/hr, find the time taken by the boat to go 68 km downstream.
2 hours
3 hours
4 hours
5 hours
Explanation:

Speed downstream = (13 + 4) km/hr = 17 km/hr.

Time taken to travel 68 km downstream =$ \left(\dfrac{68}{17} \right) $hrs = 4 hrs.
2464.If a mans rate with the current is 15 km/hr and the rate of the current is 11/2 km/hr, then his rate against the current is
12 km/hr
10 km/hr
10.5 km/hr
12.5 km/hr
Explanation:

Speed downstream = 15 km/hr

Rate of the current= 11/2 km/hr

Speed in still water = 15 - 11/2 = 131/2 km/hr

Rate against the current = 131/2 km/hr - 11/2 = 12 km/hr

2465.The speed of the boat in still water in 12 kmph. It can travel downstream through 45 kms in 3 hrs. In what time would it cover the same distance upstream?
8 hours
6 hours
4 hours
5 hours
Explanation:

Speed of the boat in still water = 12 km/hr

Speed downstream $=\dfrac{45}{3}$ = 15 km/hr

Speed of the stream = 15-12 = 3 km/hr

Speed upstream = 12-3 = 9 km/hr

Time taken to cover 45 km upstream $=\dfrac{45}{9}$ = 5 hours

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