Question

10. 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 still water.​

Answer 1

Answer:

speed of stream = 8 km/h

speed of boat = 3km/h

Step-by-step explanation:

Let speed of boat in still water = y

Let speed of stream = x

Accordingly,

$(x + y) = \frac{44}{4} \: .....equation \: 1$

$(x - y) = \frac{20}{4}</u> <u>$ ......equation 2

therefore,

(x+y) = 11............ equation 3

(x-y) = 5.............. equation 4

by (3) + (4),

x+y+x-y = 16

=) 2x = 16

=) x = 8

From equation 3,

8+y = 11

=) y = 3

Hope it helps.

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