Question

A boat takes 4 hours to go 44 km downstream and it can go 20 km upstream in the same time. Find the speed of the stream and that of the boat in the still water

Answer 1

Answer:

Speed of stream=8 km/h

Speed of boat in the still water=3 km/h

Step-by-step explanation:

Let the speed of the stream=x km/h

Let the speed of the boat in still water=y km/h

Downstream

x+y=44/4

x+y=11....(1)

Upstream

x-y=20/4

x-y=5.....(2)

On solving (1) and (2)

2y=6

y=6/2=3 km/h

x=8 km/h

Speed of stream=8 km/h

Speed of boat in the still water=3 km/h

Answer 2

Answer:

Speed of stream = 3 km/h

Speed of boat in still water = 8 km/h

Step-by-step explanation:

Let the speed of stream be y km/h and boat be x km/h.

✏ Downstream:

Distance = 44 km

speed = (x + y) km/h

∴ time, t1 = distance/speed = 44/x + y

i.e., 4 = 44/x + y

$\:$

∴ x + y = 11 → (1)

✏ Upstream:

Distance = 20 km

speed = (x - y) km/h

time, t2 = 20/x - y

i.e., 4 = 20/x - y

∴ x - y = 5 → (2)

Now, (1) + (2) ⇒

⇝ 2x = 16

⇝ x = 16/2

⇝ x = 8

Substituting the value of x in (1) ⇒

⇝ 8 + y = 11

⇝ y = 11 - 8

⇝ y = 3

i.e., speed of stream = 3 km/h

speed of boat in still water = 8 km/h