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November 26, 2008

Age puzzle

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as it was 4 years ago, because an old member has been
replaced by a young member.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
he new member ?


Secret Squïrrel said...

The average age of the group is calculated by adding up all of their individual ages and dividing by the number of members, in this case 10. Four years later, all of the members are 4 years older so the sum of their new ages is 4 * 10 = 40 more than before.

So, in order to make the average the same as before you would have to somehow subtract this extra 40. Therefore the new member is 40 years younger than the one he replaced.

Anonymous said...

the average age of team member

years ago is 72*10 /10 =72 (10 members)

Now 76*9=684(9 members) + 36 (y member) /10 =72