Question

Boat takes 128 min less to travel to 48 Km downstream than to travel the same distance upstream. If the speed of the stream is 3 Km/hr. Then Speed of Boat in still water is?​

Answer 1

Answer:

Speed of the stream=3km/hr

Let the speed of the boat in still water be x km/hr

Downstream speed of the boat=x+3

Upstream speed of the boat=x-3

Therefore, [48/(x-3)] - [48/(x+3)] = 128/60

or, 6/(x^2–9) = 128/(60*48)

or, x^2–9 = 135

or, x^2 =144

or, x=12 km/hr

Hence, the speed of the boat in still water is 12km/hr

Answer 2

Answer:

The speed of the boat in still water is 12 km/hr

Step-by-step explanation:

Let the speed of the boat in still water be x

Let the speed of the river be y

So, when the boat is going upstream the speed will be x - y

So, when the boat is going downstream will be x + y

Distance / speed = time

The boat takes 128 min less to travel to 48 Km downstream than to travel the same distance upstream

48 / x - y

{48/(x - y)} - {48/(x+y)} = 128/60

( 128 is in mins so divide it by 60 to convert into hours)

96x/(x^2 - y^2)  = 128/60

5760x/128 = x^2 - y^2

45x = x^2 - y^2

The speed of the river is 3 km/hr

135 = x^2 - 9

144 = x^2

x = 12

The speed of the boat is 12 km/hr