A free original bilingual lesson for the Ratios Percentages and Commercial Comparisons module of RRB Group D Mathematics. Use the stated positive total cost as the profit or loss base and marked price as the discount base. Follow forward and reverse price calculations, markup followed by discount, successive discounts and combined sales. Eight worked cases make each price base and condition explicit. Entry checks, coached examples, an analogy, a quick reference and 12 practice questions with explained answers support learning. This PDF covers this topic only, not the complete Mathematics syllabus or a full CBT simulation.