If you can afford ₹500, buy the legal e-book. It gives you peace of mind, regular updates, and no malware risk. If you cannot afford it, use a physical copy from a library or a second-hand book—not a pirated PDF.
The book typically arranges problems as:
Attempt Level 1 first. Only after scoring 80%+ should you move to Level 2. Level 3 is optional for most aspirants.
If you possess a copy or have access to the PDF, follow these tips to maximize your output: