Combined mean for multiple groups: x̄combined = (n₁x̄₁ + n₂x̄₂ + ...)/(n₁ + n₂ + ...). Example: Class A (25 students, mean 75) and Class B (30 students, mean 82). Combined mean = (25×75 + 30×82)/55 = (1875 + 2460)/55 = 78.8. Solving: Calculate total of each group (ni × x̄i). Sum totals. Divide by total students. Applications: Combining department results, pooling samples. Advantage: One combined statistic. Disadvantage: Loses individual distribution info. Exam tip: Don't average the means directly; weight by group size. Practice: Multiple group scenarios.