Introduction:
Yes, using previous years' papers is an excellent strategy to practice numerical and calculation-based questions for UPSC exams. These papers provide valuable insight into the type of questions that have been asked in the past, allowing you to familiarize yourself with the exam pattern and gain confidence in solving similar problems. Let's delve into the details of why and how you should use previous years' papers for practice.

Benefits of using previous years' papers:
1. Understanding the exam pattern: By solving previous years' papers, you can gain a clear understanding of the exam pattern, the distribution of marks across different topics, and the level of difficulty for numerical and calculation-based questions. This knowledge will help you strategize your preparation effectively.

2. Identifying important topics: Going through previous years' papers will help you identify the topics that are frequently asked in the exam. This allows you to prioritize your preparation and focus more on those areas that have a higher chance of being tested.

3. Improving time management: Solving previous years' papers under timed conditions will enhance your speed and accuracy. It will train you to allocate the appropriate amount of time to each question, ensuring that you complete the paper within the given time limit.

4. Building confidence: Regular practice with previous years' papers will build your confidence in solving numerical and calculation-based questions. As you become more familiar with the question types and develop effective problem-solving strategies, you will feel more prepared and confident on the exam day.

How to use previous years' papers effectively:
1. Start with a diagnostic test: Begin by taking a diagnostic test using a previous year's paper. This will help you assess your current level of preparation and identify your strengths and weaknesses.

2. Thoroughly analyze the solutions: After attempting a previous year's paper, carefully analyze the solutions provided. Understand the steps and techniques used to solve the problems. Identify any gaps in your knowledge or areas where you made mistakes.

3. Practice regularly: Set aside dedicated study time to solve previous years' papers regularly. Gradually increase the difficulty level as you become more comfortable with the questions. Time yourself to simulate exam conditions and track your progress.

4. Review and revise: After solving a paper, review your answers and identify the areas where you made mistakes. Revise those concepts and practice similar questions to reinforce your understanding.

5. Seek guidance if needed: If you encounter difficulties while solving the previous years' papers, seek guidance from your teachers, mentors, or online educational platforms like EduRev. They can provide clarifications, explain concepts, and offer alternative problem-solving approaches.

In conclusion, using previous years' papers for practicing numerical and calculation-based questions is a highly effective strategy for UPSC exam preparation. It helps you understand the exam pattern, identify important topics, improve time management, and build confidence. By following a systematic approach and regularly practicing with these papers, you can significantly enhance your problem-solving skills and increase your chances of success in the UPSC exam.