# Aptitude - Boats and Streams - Discussion

### Discussion :: Boats and Streams - Data Sufficiency 2 (Q.No.1)

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.

1.

 What is the speed of the boat in still water? I. The speed downstream is 12 kmph. II. The speed upstream is 4 kmph. III. In a to and fro journey between two points, the average speed of the boat was 6 kmph.

 [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

Explanation:

 From I and II, speed of boat in still water = 1 (12 + 4) km/hr = 8 km/hr. 2

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. 2

Similarly, I and III also give the answer. Correct answer is (D).

 Tarandeep said: (Nov 26, 2012) How this formula for Avg Speed is calculated?

 Amit said: (Nov 9, 2013) 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.

 Aman said: (Dec 3, 2013) Can anybody tell me how we get the value 4 in that average speed formula you have putted.

 Aashit said: (Jun 25, 2014) Why has 4 been substituted for 'x' when 4=x+y?

 Rahul said: (Feb 15, 2015) x is the speed of the boat upstream, and y is the speed of the boat downstream.

 Swarnashree said: (Aug 28, 2015) Why x is taken as speed of the boat upstream?

 Shashi said: (Oct 22, 2016) How is statement 3 related to question? There is no need of 3rd statement or no relation b/w 3rd to another statement.

 Harshavardan said: (Jan 10, 2017) 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".

 Priya said: (May 6, 2018) 123+45=168, 168*0=0, 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.

 Abhilasha said: (Jul 17, 2018) 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.

 Kapadiya Sagar said: (Jun 26, 2020) Options 1 and 3 become same. a+b = 6kmph. So with one equation two unknown is not solvable. So, the Correct option is [A].