BEST 5 Shortcuts on Boats and Stream Problems for SBI Clerk / IBPS Exams 2017

BEST 5 Shortcuts on Boats and Stream Problems for SBI Clerk / IBPS Exams 2017
BEST 5 Shortcuts on Boats and Stream Problems for SBI Clerk / IBPS Exams 2017:
Dear Readers, Here we have given the BEST 5 Shortcuts on Boats and Stream Problems for SBI Clerk / IBPS Exams 2017, candidates those who are preparing for the upcoming SBI Clerk/IBPS Exams 2017 can make use of it.


BASIC CONCEPT OF BOATS AND STREAM
Still water:
If the water is not moving then it is called still water.
Speed of boat in still water is= ½ (Downstream Speed + Upstream Speed)
Stream:
Moving water of the river is called stream
Upstream:

If a boat or a swimmer moves in the opposite direction of the stream then it is called upstream movement. In this case motion of boat or swimmer isopposedby the motion of stream.
Downstream:

If a boat or a swimmer moves in the same direction of the stream then it is called downstream movement. In this case motion of boat or swimmer issupported by the motion of stream.

When speed of boat or a swimmer is given then it normally means speed in still water.
Concepts and formulas of boats and streams are also applicable to problems involving:
Cyclist and wind:
Cyclist analogous to boat and wind analogous to stream.
Swimmer and stream:
Swimmer analogous to boat
If speed of boat in still water is ‘b’ km/hr and speed of stream is ‘s’ km/hr,
Speed of boat downstream = (b+s) km/hr, since the boat goes with the stream of water hence its speed increase.
Speed of boat upstream = (b – s) km/hr.the boat goes against the stream of water and hence its speed gets reduced.
Distance = Speed × Time
D = ST

Type 1:
If Ratioof downstream and upstream speeds of a boat is a : b. then ratio of time taken = b : a
Speed of stream = ((a – b)/ ( a + b))× speed in still water.
Speed in still water = ((a + b) /(a – b)) × speed of stream.
Example:
1) A man can row a boat to a certain distanced upstream in 4 hours and takes 3 hours to row downstream the same distance. What is the speed of boat in still water, if the speed of the stream is 2 km/hr?
a) 9km/hr    b) 10 km/hr    c) 12 km/hr     d) 14 km/hr
Solution:
Ratio of speed downstream and upstream = 3 : 4
Speed of boat in still water = ((4+3) / (4-3)) × 2 = 14 km/hr
2) A man can row a boat 120 km with stream in 5 hours. If speed of the boat is double the speed of the stream, find the speed stream?
a) 6 km/hr    b) 8 km/hr    c) 9 km/hr     d) 12 km/hr
Solution:
Speed of the boat downstream = 120/5 = 24 km/hr
Ratio of speed of boat and stream = 2 : 1àspeed of stream = 1/3 *24 = 8 km/hr

Type 2:
1) If a steam boat goes 8 km upstream in 40 minutes and the speed of stream is 5 km/hr, In still water what would be the speed of the boat?
Solution:
Rate of stream = 8 x 60 / 40 = 12 km/h. [convert minutes to hour we multiplying by 60] the speed of stream is 5 km/h
Let speed in still water be x km / hr.
If stream speed 5 km then speed of upstream would be = (x – 5) km/hr
Then, speed upstream = (x – 5) km / hr.
So, x – 5 = 12
x = 12 + 5 = 17 km/hr.
Type 3:
3) Pavi rows in still water with a speed of 4.5 kmph to go to a certain place and to come back. Find his average speed for the whole journey, if the river is flowing with a speed of 1.5 kmph ?
Solution:
Pavi’s speed upstream = 4.5 – 1.5 = 3 kmph
Pavi’s speed downstream = 4.5+1.5 = 6 kmph
Distance = X km 
Time Taken in upstream = X/3 
Time Taken in downstream = X/6
Average Speed = 2X/(X/3 + X/6 ) = 4 kmph 
Type 4:

When a boat’s speed in still water is ‘a’ km/h and river is flowing with a speed of ‘b’ km/h an time taken to cover the same distance downstream, then 

Example:
1)A boat’s speed in still water is 10 km/h while river is flowing with speed of 2 km/h and time to cover a certain distance upstream is 4 h more than time taken to cover the same distance downstream. Find the distance.
Solution:
        Here, a =10 km/h, b = 2 km/h, T = 4 h
        By using formula:
        Required distance = [(10^2 – 2^2)/(2×2)]x4
                     = 96 km

Type 5:
Speed of boat in still water& speed of stream are given. Find average speed of boat that covers certain distance& returns through the same path.
Example:
1) If the speed of boat in still water is 10 km/hr& the speed of stream is 3 km/hr, the boat rows to a place which is 50 km far& returns through the same path. What would be the average speed of boat during the journey?
a) 2 km/hr    b) 4.5 km/hr    c) 9.1 km/hr   d) 15 km/hr
Solution:
If a boat moves at ‘x’ km/hr speed and covers the same distance up and down in a stream at the speed of ‘y’ km/hr, then average speed is calculated by,
Speed of boat in still water = x = 10 km/hr
Speed of stream = y = 3 km/hr
We have,
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