Multiple choice

The average age of a group of some persons is 16.75 years. By joining 20 new persons with an average age of 13.25 years, the average age of the group becomes 15 years. Find out the number of persons in the group initially.

  1. 29

  2. 20

  3. 28

  4. 32

  5. 26
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Let initial persons be x with average 16.75, so sum = 16.75x. After 20 persons with average 13.25 join, total persons = x + 20, sum = 16.75x + 20×13.25, and new average = 15. So 16.75x + 265 = 15(x + 20). Solving: 1.75x = 35, so x = 20.

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