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The average age of 10 members of a committee is the same as it was 4 years ago, because an old member has been replaced by a young member.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. 30 years

  2. 40 years

  3. 80 years

  4. 60 years

Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

4 years ago, the total age of 10 members was 10 years less than today (10 × 4 = 40). For the average to stay the same after one replacement, the new member must be 40 years younger than the replaced member. This compensates exactly for the 40 years that the other 9 members collectively aged. Option A (30 years) and D (60 years) don't balance the equation.