Question

If a boat goes down streat it covers 30km in 5hrs. And if goes upstream it covers 10 km in

5hrs . Find speed of boat in still water and speed of stream.​

Answer 1

Step-by-step explanation:

the total speed of the boat is 600

then it was still in water then the speed was 20

Answer 2

Let the speed of the stream =x km/hr

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

Upstream speed =y−x km/hr

Downstream speed =y+x km/hr

time=

speed

distance

The boat goes 30 km upstream and 44 km downstream in 10 hours.

Time taken =

y−x

30

+

y+x

44

10=

y−x

30

+

y+x

44

(1)

The boat goes 40 km upstream and 55 km downstream in 13 hours.

Time taken =

y−x

40

+

y+x

55

13=

y−x

40

+

y+x

55

(2)

Let

y−x

1

=u

and

y+x

1

=v

From (1) and (2),

30u+44v=10 (3)

40u+55v=13 (4)

Multiply equation (3) with 4 and equation (4) with 3,

120u+176v=40 (5)

120u+165v=39 (6)

subtract equation (6) from (5),

176v−165v=40−39

11v=1

v=

11

1

⇒

y+x

1

=

11

1

y+x=11 (7)

From equation (3),

30u=10−44v

30u=10−44×

11

1

30u=10−4=6

u=

5

1

y−x

1

=

5

1

⇒y−x=5 (8)

Adding (7) and (8), we get,

2y=16

y=8

From equation (7),

x=11−y

x=11−8=3