Multiple choice

9 years ago, the average age of a family of five members was 33 years. Now, three new members join whose ages are in ascending order with consecutive gaps of 8 years. If the present average age of the family is the same as it was 9 years ago, what is the age (in years) of the youngest new member?

  1. 15

  2. 30

  3. 10

  4. 12
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

9 years ago: 5 members, average 33, total = 165. Now those 5 members are 165 + 5×9 = 210 years old. Current average is still 33 with 8 members, so current total = 8×33 = 264. Three new members' total age = 264 - 210 = 54. Ages in AP with gap 8: let ages be a, a+8, a+16. Sum = 3a + 24 = 54, so 3a = 30 and a = 10.

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