Question

A motor boat takes 1 hour more to go 12 km upstream than to return downstream to
the same spot. Find the speed of the boat in still water if the speed of the stream is
1 km/hr.​

Answer 1

Answer:

T = time for downstream,

t = time for upstream travel.

T + t = 3 hrs 45 min = 15/4 hrs.

For downstream, distance/velocity = time,

15/(V + v) = T

15/(9 + v) = T ... (1)

Similarly,

15/(9 - v) = t ... (2) ,where V - Speed of boat, v - speed of stream.

Add (1) and (2)

15/(9 + v) + 15/(9 - v) = T + t

15(18)/(81 - v2) = 15/4

v2 = 81 - (18x4) = 9

v = sped of stream is 3 km/hr.

Step-by-step explanation:

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Answer 2

Answer:

Let the speed of the stream be x km\hr.

The speed of the boat upstream = (18 - x) km/hr

The speed of the boat downstream = (18 + x) km/hr

Distance = 24 km

As given in the question,

Time for upstream = 1 + Time for downstream

24/(18 - x) = 1 + 24/(18 + x)

24/(18 - x) - 24/(18 + x) = 1

x2 + 48x - 324 = 0

(x + 54)(x - 6) = 0

x ≠ - 54 as speed cannot be negative.

x = 6

The speed of the stream = 6 km/hr

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