Arithmetic aptitude :: Boats and Streams :: Data Sufficiency 2

• Boats and Streams - General Questions
• Boats and Streams - Data Sufficiency 1
• Boats and Streams - Data Sufficiency 2
• Boats and Streams - Important Formulas and Facts

Still water : The speed of water in the river is zero.

Stream water : The water in the river is flowing or moving.

Speed of Boat and Stream :

Assume the man's rate of rowing in still water $=x$ km/hr Speed of stream $= y$ km/hr

(a) Down stream rate $=(x+y)$ km/hr

(i.e.) direction of rowing and direction of flow is same.

(b) Up stream rate $=(x-y)$ km/hr

(i.e.) direction of rowing and direction of stream are opposite. Speed of still water and stream : Assume, speed downstream $=a$ km/hr

Speed upstream $=b$ km/hr

Then, speed in still water $=\frac{1}{2}(a + b)$ km/hr

Rate of stream $=\frac{1}{2}(a - b)$ km/hr

Find the speed of the man in still water ?

I. The downstream speed is $12$ km/hr.

II. The upstream speed is $4$ km/hr.

III. In a back-and-forth travel between two points, $A$ and $B$, the average speed of the man was $6$ km/hr.

Answer:

Explanation:

From I and II, speed of the man in still water $=\frac{1}{2}(12+4)$ $=8$ km/hr.

From II and III, we get:

Average speed $=\frac{2xy}{x+y}$

$\Rightarrow \frac{2\times 4\times y}{4+y}$ $=6$

$\Rightarrow 8y$ $=24+6y$

$\Rightarrow y$ $=12$.

$\therefore$ Required speed $=\frac{1}{2}(12+4)$ km/hr $=8$ km/hr.

Similarly, I and III also give the answer.

$\therefore$ Correct answer is (D).

• Boats and Streams - General Questions
• Boats and Streams - Data Sufficiency 1
• Boats and Streams - Data Sufficiency 2