### Discussion :: Boats and Streams - General Questions (Q.No.5)

Ashok said: (Jul 19, 2011) | |

From where do this 1/2 came from? |

Vivek Patidar said: (Sep 5, 2011) | |

Because in the condition of still position of water the speed one side and opposite side of water will be equal thats why we will take average of both speed. |

Manjit Singh said: (Sep 15, 2011) | |

Here speed along the stream and against the stream is given. Then how can we assume water to be steady (both the ways). Then why this 1/2 has come? |

Debapriya Dandapat said: (Sep 17, 2011) | |

Upstream relative speed is u + v=11km/hr Downstream speed is u-v=5 Where u= speed of boat in still water and v is speed of stream So adding two equations u+v + u-v =11+5 2u=16 So, u=8. |

Ajit Jha(Iit Kharagpur) said: (Dec 30, 2011) | |

This Q is wrong buddy... Here in stream dir. it takes 1 hour and again in downstream it takes 1 hour. Then.. x+y=11/1=11------(1) x-y=5/1=5----(2) fm eq. 1 & 2.. we get.. x=8 km/h |

Saloni Nautiyal said: (Feb 25, 2012) | |

Formula for speed of boat in still water=[(X+Y)+(X-Y)]/2 where X=SPEED OF BOAT IN STILL WATER Y=SPEED OF STREAM/CURRENT THEREFORE, [(11+5)+(11-5)]/2=11 ANSWER=11 ANSWER IS NOT IN THE OPTIONS |

Kottitheking said: (Sep 9, 2012) | |

Upstream relative speed is u + v=11km/hr Downstream speed is u-v = 5 Where u = speed of boat in still water and v is speed of stream Then adding two equations u+v + u-v =11+5 2u=16 Finally, u=8. |

Brinda Iyer said: (Mar 10, 2013) | |

But if in the same question distance traveled is asked, then what is the formula? |

Ritha Epsiba said: (Mar 13, 2013) | |

If the speed of a boat in still water is u km/hr and the speed of the stream is v km/hr, then: Speed downstream = (u + v) km/hr. Speed upstream = (u - v) km/hr. |

Arun.D said: (Jun 3, 2013) | |

Downstream=11km/hr. Upstream=5km/hr. Speed in still water = 1/2(a + b) km/hr. a = upstream. b = downstream. Speed = 1/2(11+5)km/hr. = 1/2(16)km/hr. = 8km/hr. |

Mina said: (Jan 7, 2015) | |

What is u and v? |

Subaram said: (Jan 8, 2015) | |

Here direction along the stream called downstream and against the stream called upstream. In this question they gave along the stream 11 kmhr against the stream 5 kmhr. So speed still in water = 1/2 (a+b) , here a downstream be up stream as for formula. |

Naresh said: (Apr 28, 2015) | |

Given that, Speed in the downstream (d) = 11 km/hr. Speed in the upstream (u) = 5 km/hr. Speed of the Boat in still water = d + u/2. => 11 + 5/2 = 16/2. => 8 km/hr. |

Ramachandran said: (May 28, 2015) | |

Hello guys how would you find: 11 km/hr is Downstream. 5 km/hr is Upstream. |

Suchita said: (Aug 9, 2015) | |

Because in question they have mentioned speed of boat along the stream (i.e downstream) is 11km/hr and against the stream (i.e upstream) is 5km/hr. |

Nikul Rana said: (Nov 1, 2015) | |

Speed downstream = X+Y = 11 kmph; Speed upstream = X-Y = 5 kmph; Speed of the still water = (X+Y)+(X-Y)*1/2 = 8 kmph. |

Priya said: (Dec 10, 2015) | |

What is this? Am not clear, I am late pick up person, say clearly guys. |

Nija said: (Jan 18, 2016) | |

In this question, it is not mentioned whether 1 hour each taken by downstream and upstream. So how can we solve this questions ? Please am confused. |

Ayan said: (Apr 13, 2016) | |

The question is not clear. It says in one hour both travel upstream as well as downstream. How is it explain me? |

Shruti said: (Jun 22, 2016) | |

How come the speed becomes 11 kmph and 5 kmph when only distance is given, and boat travels both the distances in total 1 hour? I think either the question is wrong or 8 is not the answer. |

Shudhu said: (Jul 31, 2016) | |

Downstream so, x + y = 11. Upstream so, x - y = 5. Solve equation 1 and 2. You get x =7.5. So, nearest answer is 8. |

Sara said: (Jan 2, 2017) | |

x = speed of stream still in water. y = speed of stream. downstream = Distance/ X+Y = Time, = 11/ X+Y = 1hour. Upstream= Distance/ X-Y = Time. = 5/X-Y = 1hour. Cross multiply 11 = X + Y -----(1)eq 5 = X - Y ------(2)eq We need x, so cancel y. 2X = 16, X = 8kmph. |

Aman Kumar said: (Jan 27, 2017) | |

B = Speed of boat. w = Speed of water. NOW B + W=11 (with the stream) B - W=5 (opp to stream) ---------------- 2B =16, B =16/2, = 8 KMPH. |

Suresh said: (Feb 26, 2017) | |

A boats cover 1 km in 10 minute with stream and 1 km in 20 minute against stream now speed of boat in still water will be? Please solve it. |

Audry said: (Mar 15, 2017) | |

Let U= speed of boat in still water and v=speed of stream then; Upstream speed, U - V = 5km/hr, Downstream speed, U + V = 11km/hr, Eqt, U + V + U - V = 11 + 5 2U = 16 U = 16/2 = 8km/hr. |

Satish said: (Jun 17, 2017) | |

D=11 U=5. (D+U)/2=x. 11+5/2=X. 16/2=X. 8=X (stream speed). |

Bhavesh said: (Aug 12, 2017) | |

What is this same Q is like in 3 hours a boat goes 11 km along the stream and 5 km against the stream the speed of the boat in still water is? |

Kamala Kant said: (Sep 11, 2017) | |

Do you have the concept of eqillibrium? then say if , (11/x +y) + (5/x-y) =3, x=? |

Yamini said: (Oct 26, 2017) | |

If the speed downstream is a km/hr and speed upstream is b km/hr then, Speed in still water=1/2(a+b)km/hr. |

Rz Reddy said: (Nov 4, 2017) | |

Downstream(D). Upstream so(U). D+U = 11. D-U = 5. 2D = 16. D = 16/2. D = 8km/hr. |

Nurun Nobi Khokon said: (May 23, 2018) | |

Let, downstream (with stream) speed= x. upstream (against) speed is= y. Now, x = speed of the boat+speed of the water. y = speed of the boat-speed of water. ----------------------------------------------------------- x+y = 2*speed of the boat. So, speed of the boat = (x+y)/2 [downstream speed+upstream speed]. |

Hari said: (Jun 11, 2018) | |

For finding the speed of the boat in still water = (upstream-downstream/2). For finding water speed = (upstream+downstream/2). |

Shandeepsamy said: (Jul 2, 2018) | |

Where this 1/2 came from? Please explain. |

Darkele said: (Jul 4, 2018) | |

Note, there is no use of the 1 hour given because the upstream and downstream is sufficient to get the speed of the boat in still water. |

Vinau said: (Sep 5, 2018) | |

X+Y=11, X-Y=5, X+Y+X-Y=11 + 5, 2X=16. Then, X=8. |

A.K.Balakrishnan said: (Sep 13, 2019) | |

@All. Follow this method for all boat question; Downstream means boat towards the down in this situation we have to find the speed of boat and speed of stream. Let x be boat speed. Let y be stream speed. 1) Down stream speed = D/T(downstream time) = x+y note: distance will be the same as both the streams. 2) Upper stream speed = D/T (upper stream time) = x-y. Thank you. |

Musoyiti said: (Jun 6, 2020) | |

My way of solving is that; Let the speed of the current be x. So the speed in still water will be 11-x and 5 +x. Now as these both expressions are same so we use linear equation and find the value of x to be 3. So the speed of the current is 3 km/hr. So the speed of the boat in still water is 11-3=8. Hence it is 8 km/hr. |

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