In Class I, there are 12 students of average age 20 years and in Class II, there are 16 students of average age 23 years. What will be the approximate average age for all the students of these two classes?
21.7 years
The correct answer is 21.7 years.
The formula for weighted average is: $$\text{Weighted Average} = \frac{w_1 x_1 + w_2 x_2 + \dots + w_n x_n}{w_1 + w_2 + \dots + w_n}$$ Where x_i is the average of group i, and w_i is the weight (in this case, the number of students) for group i. The combined average age will always be between the two individual averages (20 and 23 years) and will be closer to the average of the larger group (Class II with 16 students and average 23).
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