Question

A boat can row 1 km with stream in 10 minutes and 1 km against stream in 20 minutes. what is the speed of the boat in stll water?

a.1.5 km/hr

b.3 km/hr

c.3.4 km/hr

d.4.5 km/hr

Answer 1

Answer:

The speed of the boat in still water is 4.5 kmph

Step-by-step explanation:

Given : A boat can row 1 km with stream in 10 minutes and 1 km against stream in 20 minutes.

To find : What is the speed of the boat in still water?

Solution :

Speed of water in the upstream and downstream,

Let downstream(u) is

1÷10÷60=6 kmph

Let upstream(v) is

1÷20÷60=3 kmph

Speed of the boat in still water,

s=u+v÷2

s=6+3÷2

s=9÷2

s=4.5

Therefore, Option d is correct.

The speed of the boat in still water is 4.5 kmph.

Answer 2

Given :  A boat can row 1 km with stream in 10 minutes and

1 km against stream in 20 minutes.

To Find : The speed of the boat in still water?

a.1.5 km/hr b.3 km/hr c.3.4 km/hr d.4.5 km/hr​

Solution:

Distance = speed * time

10 mins = 10/60 hrs

20 mins = 20 /60 hrs

speed of the boat in still water = x  km/hr

speed of the stream = y  km/hr

speed of the boat  with stream = x + y km/hr

x + y   = 1/(10/60)  

=> x + y  = 6

speed of the boat against stream = x - y km/hr

x + y   = 1/(20/60)  

=> x - y  = 3

Adding both

=> 2x = 9

=> x = 4.5

The speed of the boat in still water is 4.5 km/hr

Correct option is d) 4.5 km/hr

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