Aptitude - Boats and Streams - Discussion

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

Each of the questions given below consists of a question followed by three statements. You have to study the question and the statements and decide which of the statement(s) is/are necessary to answer the question.


What is the speed of the boat in still water?


The speed downstream is 12 kmph.


The speed upstream is 4 kmph.


In a to and fro journey between two points, the average speed of the boat was 6 kmph.

I and II only
All I, II and III
III, and either I or II
Any two of the three
None of these
Answer: Option

From I and II, speed of boat in still water = 1 (12 + 4) km/hr = 8 km/hr.

From II and III, we get:

Using average speed = 2xy , we get: 2 x 4 x y = 6
x + y 4 + y

8y = 24 + 6y

y = 12.

Required speed = 1 (12 + 4) km/hr = 8 km/hr.

Similarly, I and III also give the answer.

Correct answer is (D).

11 comments Page 1 of 2.

Kapadiya sagar said:   4 years ago
Options 1 and 3 become same.

a+b = 6kmph.

So with one equation two unknown is not solvable.

So, the Correct option is [A].

ABHILASHA said:   6 years ago
3rd statement itself is enough as [(u+v)+(u-v)]/2=6.

Which gives u = 6; where u is the speed of the boat in still water and v is the speed of the stream.

Priya said:   6 years ago
Therefore the answer is 0.
But unfortunately, the answer is not 0.
Because any answer cannot be 0.

So, we increment the answer by 1 to avoid any problems.
Therefore the answer is 1.

HarshaVardan said:   7 years ago
My Analysis.

Upstream is 4kmps and downstream is 12kmps.
Boat speed still in water =(down stream+upstream)/2 = (1/2) * (12+4) = 8kmps.
Boat speed against the water =(down stream-upstream)/2 = (1/2) * (12-4) = 4kmps.
So, Statments 1&2 are efficient to get this answer.
Answer is Option "A".

Shashi said:   7 years ago
How is statement 3 related to question?

There is no need of 3rd statement or no relation b/w 3rd to another statement.

Swarnashree said:   8 years ago
Why x is taken as speed of the boat upstream?

Rahul said:   9 years ago
x is the speed of the boat upstream, and y is the speed of the boat downstream.

AASHIT said:   10 years ago
Why has 4 been substituted for 'x' when 4=x+y?

Aman said:   1 decade ago
Can anybody tell me how we get the value 4 in that average speed formula you have putted.

Amit said:   1 decade ago
Avg. speed = Total distance / Total time = 2L / t1 + t2.

Time = distance / speed so, t1 = L / x and t2 = L / y.

t1 + t2 = L(x+y) / xy.
Total time = L(x+y) / xy.
Total distance = 2L.

Avg. speed = 2xy/x+y.

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