A diver rowing at the speed of 3 km/h in still water takes double the time going 50 km upstream compared to going 50 km downstream. The speed of the diver downstream is:

Correct option is B

Given: 

Speed of the diver in still water = 3km/h 

Time taken upstream = 2 $$\times$$ time taken downstream     

Distance both upstream and downstream = 50 km./h

Solution:

Let the speed of stream = x km/h

​$$\frac{\frac{50}{3 +x}}{\frac{50}{3 - x}}= \frac{1}{2}$$ 

$$\frac{3 - x }{3+x} = \frac{1}{2}$$ 

6 - 2x = 3 + x 

3 = 3x 

x = 1 km/h   

Downstream speed =  3 + 1 = 4 km/h​