The average age of the boys in a class is 16 years and that of the girls is 15 years. The average age for the whole class is

### Concept & Logic To calculate the combined or weighted average of two distinct groups, you need two pieces of information: the individual average of each group, and the relative weights (i.e., the ratio or exact number) of elements in each group. ### Step-by-Step Solution * **Given:** Average age of boys = 16 years. Average age of girls = 15 years. * **Missing Data:** Let the number of boys be $B$ and the number of girls be $G$. * **Formula:** The formula for the class average is: $$Class \ Average = \frac{16B + 15G}{B + G}$$ * **Deduction:** Without knowing the values of $B$ and $G$, or at least their ratio ($B:G$), it is impossible to evaluate this fraction. Therefore, the exact average cannot be determined. ### Exam Strategy & Shortcut When reading weighted average problems, immediately scan for quantities or ratios. If you see group averages but no mention of "how many" are in each group, jump straight to "Cannot be determined". No calculation is needed. ### Common Pitfall The most common trap is assuming there are an equal number of boys and girls in the class. If $B = G$, the average would be the simple mean: $\frac{16 + 15}{2} = 15.5$ years. The test setter included 15.5 years as an option precisely to catch students making this unfounded assumption. ### Final Answer Therefore, the correct answer is Cannot be computed with the given information.