A free original bilingual lesson for the Numbers and Calculation module of RRB Group D Mathematics. Learn how natural numbers, whole numbers, integers and rational numbers are related; compare signed integers; and explain arithmetic signs, grouping, powers, equal-precedence operations and division by zero. Entry checks, worked examples, an analogy, a quick reference and 12 practice questions with explained answers support step-by-step learning. This PDF covers one foundation topic, not the complete Mathematics syllabus or a full CBT simulation.