Difficulty: Medium
Correct Answer: 401/3 yr
Explanation:
Introduction / Context:
When a group’s average increases after replacement without changing the headcount, the total age increases by (increase in average) * (group size). That increase must come from the difference between the incoming and outgoing members’ totals.
Given Data / Assumptions:
Concept / Approach:
Let W be the sum of the three women’s ages. Then W − 99 = 22 → W = 121. The average of the three women is W / 3.
Step-by-Step Solution:
Increase in total = 22W − 99 = 22 → W = 121Average (women) = 121 / 3 = 40 1/3 years
Verification / Alternative check:
Replacing 99 by 121 raises the committee total by 22, which across 11 members raises the mean by exactly 2 years.
Why Other Options Are Wrong:
40, 41, and 39 2/3 do not produce the exact +22 total change; 411/3 is a misread of the mixed fraction needed here (correct is 401/3).
Common Pitfalls:
Confusing “sum increases by 22” with “each woman is 22 years older” or misreading mixed fractions. Always compute totals first.
Final Answer:
401/3 yr
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