Discussion
Find the ratio of swimming speed of Raj in still water to speed of river, if ratio of time taken to go 10km upstream to time taken to go 10km downstream is 11:5?
Answer: C
Write \( b \) for the boat's speed in still water and \( r \) for the stream's. Then
\[ \text{downstream} = b + r, \qquad \text{upstream} = b - r \]
For a fixed distance, time is inversely proportional to speed, so the time ratio inverts to give the speed ratio:
\[ \frac{t_{\text{up}}}{t_{\text{down}}} = \frac{11}{5} \quad\Longrightarrow\quad \frac{b + r}{b - r} = \frac{11}{5} \]
\[ 5(b + r) = 11(b - r) \quad\Longrightarrow\quad 5b + 5r = 11b - 11r \]
\[ 16r = 6b \quad\Longrightarrow\quad \frac{b}{r} = \frac{16}{6} = \frac{8}{3} \]
So the ratio is \( 8 : 3 \). The 10 km cancels out, so the distance is never needed.
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