Question

(i) Ritu can row downstream 20 km in 2 hours, and upstream
4 km in 2 hours. Find her speed of rowing in still water
and the speed of the current.​

Answer 1

Answer:

Ritu can row downstream 20 km in 2 hour, and upstream 4 km in 2 hours.

Solution :-

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

                            

Upstream = (x – y) km/h                  

Downstream = (x + y) km/h                  

According to the question,                  

⇒ 2(x + y) = 20                  

⇒ x + y = 10 ... (i)                  

⇒ 2(x – y) = 4                  

⇒ x – y = 2 ... (ii)                          

Putting this equation in (i), we get                  

⇒ y = 4                  

Ritu’s speed in still water is 6 km/h

The speed of the current is 4 km/h

Step-by-step explanation:

Answer 2

Answer:

6 kmph is the speed at which Ritu rows 4 kmph is the speed of the current.  

Step by Step explanation:-

Given:

Ritu downstream is 20 km in 2 hours.

Ritu upstream is 4 km in 2 hours.

To find:

Speed of rowing in still water =?

Speed of the current =?

Solution:

The speed of the rowing on still water denoted by M kmph.

The speed of the stream denoted by N kmph.

The upstream speed of Ritu’s rowing is (M – N) kmph

The downstream speed of Ritu’s rowing is (M + N) kmph

2(M+N)=20 _______________________ (1)  

2(M-N)=4 ________________________ (2)

Solving the equation, we get  

2(M+N)=20;

2(M-N)=4;  

M-N=2;

M=2+N;

Substituting M=2+N in equation (1)

2(M+N)=20

2(2+N+N)=20 ;  

N=4  

Substituting N = 4 in equation (1),  

2(M+N)=20

2(M+4)=20

2M+8=20

2M=20-8

2M=12

M=6  

the value of M = 6.

Therefore, the speed at which Ritu rows is 6 kmph and the speed of the current is 4 kmph.