Question

motor boat whose speed is 18 km/h in still water takes 1 hr 30 minutes
more to go 36 km upstream than to return downstream to the same spot.
Find the speed of the stream.​

Answer 1

Answer: stream speed (y)=6km/hr

Step-by-step explanation:

given x=18km/hr

speed=dist/time

time=distance/speed

3/2(1 and half hour)=36/x-y-36/x+y

subs x=18 km/hr

solving this we get equation

y^2+48y-324=0

taking factors we get

y=6kms/hr and -54

as we should take only +ve values

so y=6kms/hr

Answer 2

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