Numerical or calculation-based questions can be found in the optional subjects of the UPSC exam. These questions require candidates to apply their knowledge of mathematical concepts and principles to solve problems and arrive at accurate numerical answers. While not all optional subjects have a strong emphasis on numerical calculations, there are some subjects where numerical questions are more common.

Some of the optional subjects that often include numerical or calculation-based questions are:

1. Mathematics: As the subject itself revolves around mathematical concepts and principles, it is natural to expect a significant number of numerical questions in this optional subject. Candidates are tested on their ability to solve complex mathematical problems, prove theorems, and apply various mathematical techniques.

2. Physics: Physics is a subject that involves a lot of mathematical calculations. Candidates may be required to solve problems related to mechanics, electricity, magnetism, optics, and other branches of physics. These questions often involve applying formulas, using mathematical equations, and interpreting the results.

3. Statistics: Statistics is a subject that heavily relies on numerical calculations. Candidates may be asked to analyze data, perform statistical tests, calculate probabilities, and interpret the results. These questions require a strong understanding of statistical concepts and the ability to apply them to real-world scenarios.

4. Engineering subjects: Optional subjects like Mechanical Engineering, Civil Engineering, Electrical Engineering, and others often have numerical or calculation-based questions. These questions test candidates' understanding of engineering principles, their ability to solve engineering problems, and their proficiency in applying mathematical concepts to engineering scenarios.

5. Accountancy: Accountancy is another subject that involves numerical calculations. Candidates may be asked to prepare financial statements, perform financial analysis, calculate ratios, and interpret accounting data. These questions require a deep understanding of accounting principles and the ability to apply them accurately.

In conclusion, while not all optional subjects have numerical or calculation-based questions, there are several subjects where these types of questions are common. Candidates should be prepared to apply their mathematical knowledge and problem-solving skills to solve numerical problems accurately.