Question 1086953
The average age of 10 members of a committee is the same as it was 4 years ago, because an old member has been replaced by a young member.

How younger is the new member than the older
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A = avg 4 years ago
A = (9*m + M)/10  --- M = age of the member replaced, m = avg of the other 9

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A = (9*(m+4) + N)/10  --- N = age of new member
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A = (9*m + M)/10 = (9*(m+4) + N)/10
(9*m + M)/10 = (9*(m+4) + N)/10
9*m + M = 9*(m+4) + N
9*m + M = 9*m + 36 + N
M = 36 + N
N = M - 36
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He's 36 years younger