| A river is flowing at a speed of 5 km/h in a particular direction. A man, who can swim at a speed of 20 km/h in still water, starts swimming along the direction of flow of the river from point A and reaches another point B which is at a distance of 30 km from the starting point A. On reaching point B, the man turns back and starts swimming against the direction of flow of the river and stops after reaching point A. The total time taken by the man to complete his journey is |
A) 2 h 30 min
B) 3 h 12 min
C) 3 h 30 min
D) 3 h 45 min
Correct Answer: B
Solution :
| Given, speed of the stream \[=5\,\,km/h\] |
| and speed of the man in still water \[=20\,\,km/h\] |
| \[\therefore \]Speed of the man downstream \[=20+5=25\,\,km/h\] |
| and speed of the man upstream\[=20-5=15\,\,km/h\] |
| \[\therefore \]Total time taken to complete the whole journey |
| \[=\frac{30}{25}+\frac{30}{15}=30\left( \frac{3+5}{75} \right)\] |
| \[=\frac{30\times 8}{75}=3\,\,h\,\,12\min \] |
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