Discussion
Two pipes A & B can fill a cistern in 37 1/2 minutes and 45 minutes respectively. Both the pipes are opened. The cistern will be filled in just 30 minutes if if the pipe B is turned OFF after how many minutes ..?
Answer: B
Pipe A runs for the whole 30 minutes; pipe B runs for some shorter time \( t \) before being turned off. Note \( 37\tfrac{1}{2} = \tfrac{75}{2} \), so A's rate is \( \tfrac{2}{75} \):
\[ 30 \times \frac{2}{75} + \frac{t}{45} = 1 \]
\[ \frac{60}{75} + \frac{t}{45} = 1 \quad\Longrightarrow\quad \frac{t}{45} = 1 - \frac{4}{5} = \frac{1}{5} \]
\[ t = \frac{45}{5} = 9 \text{ minutes} \]
The question asks after how many minutes B is turned off, which is this 9 - not the 21 minutes for which B is then idle.
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