Discussion
A river flows at speed of 6 km/hr. Surendra swims downstream for some distance in just 12 hours. But he takes 18 hours to return the same distance upstream. How fast is Surendra in still water?
Answer: A
Write \( b \) for the boat's speed in still water and \( r \) for the stream's. Then
\[ \text{downstream} = b + r, \qquad \text{upstream} = b - r \]
The distance is the same both ways, so the speeds are inversely proportional to the times:
\[ \frac{b + 6}{b - 6} = \frac{18}{12} = \frac{3}{2} \]
\[ 2(b + 6) = 3(b - 6) \quad\Longrightarrow\quad 2b + 12 = 3b - 18 \]
\[ b = 30 \text{ km/h} \]
Checking: downstream 36 km/h for 12 h and upstream 24 km/h for 18 h both cover 432 km.
No comment is present. Be the first to comment.
Loading…
Post your comment
Please log in or register to post a comment.
Examination Categories
- SSC Exams
- Banking Exams
- Teaching Exams
- Civil Services Exams
- Railways Exams
- Engineering Recruitment Exams
- Defence Exams
- State Government Exams
- Police Exams
- Insurance Exams
- Nursing Exams
- Other Government Exams
- NRA CET
- PG Entrance Exams
- Campus Placement
- MBA Entrance Exams
- CUET and UG Entrance
- Judiciary Exams
- Regulatory Body Exams
- Software Development