Multiple choice general knowledge math & puzzles

The average age of 10 members of a committee is the same as it was 4 years ago, because an old member has been replaced by a young member. Find how much younger is the new member ?

  1. 22

  2. 40 years

  3. 43years

  4. 36years
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

4 years ago, total age was 10 × (avg - 4) = 10avg - 40. Now total age is 10avg. The difference of 40 years equals (old member's age then) - (new member's age now). Since old aged 4 years, their current age would be 4 years more. Therefore new member is 40 years younger than current old member would be.

AI explanation

If the average age stayed the same over 4 years despite everyone naturally aging by 4 years, the total age of the group must not have increased. Without a replacement, the sum would have grown by 10 members × 4 years = 40 years. So the new member must be exactly 40 years younger than the person they replaced, to cancel out that 40-year increase and keep the average unchanged.

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