Discussion Forum



Each of the questions given below consists of three statements, numbered I, II and II respectively. Please read the question and the statements carefully and decide which of the statement(s) is/are necessary to answer the question.

1)

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.


A) I and II only

B) All I, II and III

C) III, and either I or II

D) Any two of the three

E) None of these

Answer:

Option D

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).