Aptitude - Boats and Streams - Discussion

Discussion Forum : Boats and Streams - Data Sufficiency 1 (Q.No. 2)
Directions to Solve

Each of the questions given below consists of a statement and / or a question and two statements numbered I and II given below it. You have to decide whether the data provided in the statement(s) is / are sufficient to answer the given question. Read the both statements and

  • Give answer (A) if the data in Statement I alone are sufficient to answer the question, while the data in Statement II alone are not sufficient to answer the question.
  • Give answer (B) if the data in Statement II alone are sufficient to answer the question, while the data in Statement I alone are not sufficient to answer the question.
  • Give answer (C) if the data either in Statement I or in Statement II alone are sufficient to answer the question.
  • Give answer (D) if the data even in both Statements I and II together are not sufficient to answer the question.
  • Give answer(E) if the data in both Statements I and II together are necessary to answer the question.

2.

What is the speed of the boat in still water?

I. 

It takes 2 hours to cover the distance between A and B downstream.

 II. 

It takes 4 hours to cover the distance between A and B upstream.

I alone sufficient while II alone not sufficient to answer
II alone sufficient while I alone not sufficient to answer
Either I or II alone sufficient to answer
Both I and II are not sufficient to answer
Both I and II are necessary to answer
Answer: Option
Explanation:

Let AB = x km.

 I. Speed downstream = x km/hr
2

II. Speed upstream = x km/hr.
4

Speed of boat in still water = 1 x + x km/hr.
2 2 4

Thus, I and II both even do not give the answer.

Correct answer is (D).

Discussion:
7 comments Page 1 of 1.

Sanky said:   3 years ago
AB distance is same.
Let Downstream distance be 'd' and Upstream be 'u'.
It takes 2hrs to cover downstream and 4 to cover upstream.
Dist is same, so;
Downstream speed * time = Upstream speed * time.
2d = 4u.
Therefore, d = 2u.
So,
(d+u)/2 : (d-u)/2 = 3u/2 : u/2.
i.e. 3:1.

Speed of Boat is 3 kmph.

Dinesh said:   3 years ago
I think the answer is E. Because, If the answer is D, then we didn't find the exact answer. If the answer is E we know both up&downstream time so we equate the distance and the answer will be B.S =3, S.S = 1.

D by upstream = D by downstream.
Upstream T x S = downstream T x S.
(B-S) x (4) = (B+S) x (2),
4B-2B = 4S+2S,
2B = 6S,
B = 3S,
B/S = 3/1.

Therefore B=3, S=1.

Deepak said:   4 years ago
The correct answer will be E.

Urmil said:   9 years ago
Consider this formula:

Speed of object with stream = a+b (Speed of object in still water + Speed of stream).

Speed of object against stream = a-b (Speed of object in still water - Speed of stream).

Here suppose distance traveled by boat is x km so,

As we know, Speed = Distance traveled/Time taken.

I. Speed of boat in downstream (with stream) = x/2 km/hr.

= a+b.

= Speed of object in still water + Speed of stream.

II. Speed of boat in upstream (against stream) = x/4 km/hr.

= a-b.

= Speed of object in still water - Speed of stream.

Now, if we add both the statements then,

(a+b) + (a-b) = (x/2) + (x/4).

2a = (x/2) + (x/4).

a = [(x/2) + (x/4)]/2 = ANS.

Here a is the speed of boat in still water.

Shivanath said:   9 years ago
Tell the valid reason for dividing 1/2?

Lekha L said:   1 decade ago
Can you explain why should we divide by 2?

Pavithra s said:   1 decade ago
Why do we have to divide by (1/2) ?

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