Multiple choice

There are $30$ students in a class. The average age of the first $10$ students is $12.5$ years. The average age of the remaining $20$ students is $13.1$ years. What is the average age (in years) of the students of the whole class?

  1. $18$ years
  2. $12.9$ years
  3. $14.2$ years
  4. $17$ years
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B Correct answer
Explanation

Total age = (10 * 12.5) + (20 * 13.1) = 125 + 262 = 387. Average age = 387 / 30 = 12.9 years.

AI explanation

Using the weighted average method, the total age of the first 10 students is 10 times 12.5, which equals 125 years. The total age of the remaining 20 students is 20 times 13.1, which equals 262 years. The total age of the entire class of 30 students is the sum of these two totals, or 387 years. The average age of the whole class is 387 divided by 30. The average age of the whole class is 12.9 years.

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