Find how much younger is the new member ?
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The average age of 10 members of a committee is the same as it was 4 years ago, because an old member has been replaced by a young member.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 ?
Let the sum of nine member (total) =x
and the age of old one=z
so its average 4 yrs before=(x+z)/10.
after 4 yrs let z be replaced by y.
so now avg=(x+4*10+y)/10
now (x+z)/10=(x+40+y)/10
so after solving it found
z=y+40.
so old person is 40yrs older than young one.
I would make one small adjustment to your answer. When you add 40, you’re adding the four years the retired old person aged. That shouldn’t enter into your calculation, since that person is no longer in the group. Therefore the equation should be
(x+z)/10 = (x+36+y)/10
which yields a difference of 36 years. You can test this with an arbitrary set of numbers to see that it is correct.
Agreed!
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