Question

$\huge \fbox \green{❥Question}$

A boat goes 30km upstream and 28km downstream in 10 hours. In 7 hours, it
can go 21 km upstream and 21 km downstream then to return downstream to
the same spot. Find the speed of stream and that of the boat in still water and
speed of the stream.

[Class 10 ]

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Answer 1

Answer:

ANSWER

Let the speed of the boat in still water be x km/h and speed of the stream is y km/h.

Therefore, speed of the boat while upstream is (x−y) km/h and speed of the boat while downstream is (x+y) km/h

As we know that speed=

time

distance

, therefore, time=

speed

distance

It is given that the motor boat can travel 30 km upstream and 28 km downstream in 7 hours and also it can travel 21 km upstream and return in 5 hours, thus,

x+y

30

+

x−y

28

=7.............(1)

x+y

21

+

x−y

21

=5.............(2)

Let

x+y

1

=u and

x−y

1

=v, then the equations (1) and (2) becomes:

30u+28v=7..........(3)

21u+21v=5..........(4)

Multiplying equation (3) by 21 and equation (4) by 30 we get,

630u+588v=147..........(5)

630u+630v=150..........(6)

Now subtracting equation (5) from equation (6), we get

42v=3

⇒v=

14

1

Substitute the value of v in equation (4) then, u=

6

1

Since

x+y

1

=u and

x−y

1

=v, therefore,

x+y=6..........(7)

x−y=14..........(8)

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

2x=20

⇒x=10

Hence, the speed of the boat in still water is 10 km/h.

Step-by-step explanation:

hope this will helpful to you

Answer 2

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ANSWER.....

$\huge\mathcal{\fbox{\fbox{\pink{10km/h}}}}$