1.  A man can row 7 kmph in still water. If in a river running at 1.5 km an hour, it taken him 50 minutes to row to a place and back, how far off is the place ?
A. 6 km
B. 9 km
C. 3 km
D. 4 km

Answer: Option C

Explanation:

Speed downstream = (7.5 + 1.5) kmph = 9 kmph;

Speed upstream = (7.5 - 1.5) kmph = 6 kmph.

Let the required distance be X km. Then,

X/9 + X/6 = 50/60 
<=> 2X + 3X = 5/6 x 18 
<=> 5X = 15 
<=> X = 3 
Hence, the required distance is 3 km.