A swimmer's speed in swimming pool is 6 km/hr. He swims between two points in a river and returns back to the starting point. He took 24 minutes more to cover the distance upstream than downstream. If the speed of the stream is 4 km/hr, then the distance between two points is :
Answer & explanation
Correct answer: option 2
$\text{Speed in still water}=6\text{ km/hr}.$
$\text{Speed of stream}=4\text{ km/hr}.$
$\text{Upstream speed}=6-4=2\text{ km/hr}.$
$\text{Downstream speed}=6+4=10\text{ km/hr}.$
$\text{Let distance between the points}=d.$
$\text{Upstream time}=\frac{d}{2}.$
$\text{Downstream time}=\frac{d}{10}.$
$\text{Given upstream takes }24\text{ minutes more}= \frac{24}{60}=0.4\text{ hr}.$
$\frac{d}{2}-\frac{d}{10}=0.4.$
$\frac{5d-d}{10}=0.4.$
$\frac{4d}{10}=0.4.$
$4d=4.$
$d=1.$
$\text{Distance between the points}=1\text{ km}.$