A free original bilingual lesson for the Ratios Percentages and Commercial Comparisons module of RRB Group D Mathematics. Convert between fractions, decimals and percentages; distinguish the part, rate and whole; and calculate forward, reverse and successive changes using the correct base. Compare percentage points with relative percentage change and explain why reverse comparisons need a different denominator. 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.