Multiple choice

The average age of a group of eight is same as it was 3 years ago when a young member is substituted for an old member the incoming member is younger to the outgoing member by

  1. $11\ years$
  2. $24\ years$
  3. $28\ years$
  4. $16\ years$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Over 3 years, the total age of the 8-member group would normally increase by 8 * 3 = 24 years. Since the average age remains the same after substituting the old member with the young member, the total sum of ages must also remain the same as it was 3 years ago. This means the new member's age must be exactly 24 years less than the outgoing member's current age.

AI explanation

Using the average balance method, the total required decrease in age over the 8 members to keep the overall average unchanged over 3 years is 8 multiplied by 3, which equals 24 years. Therefore, the incoming young member must be exactly 24 years younger than the outgoing old member. The difference in their ages is 24 years.

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