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Deleted Numbers (Posted on 2007-05-09) Difficulty: 2 of 5
Five numbers are selected and deleted from a set of consecutive positive integers beginning with 1. The arithmetic mean of the remaining numbers in the set is 45.1.

Find the largest possible single number that could have been deleted from the original set.

  Submitted by Dennis    
Rating: 4.6667 (3 votes)
Solution: (Hide)
Let the largest of the original numbers in the set be n with S representing the sum of the deleted numbers. Also, let v=45.1 represent the average of the remaining numbers (after the deletions).

If n, n-1, n-2, n-3, and n-4 are deleted, then the mean of the remaining numbers is (n-4)/2.

If 1, 2, 3, 4, and 5 are deleted, the mean would be (n+6)/2

--> (n-4)/2 <= v <= (n+6)/2 --> 2v-6 <= n <= 2v+4 --> 85 <= n <= 94. But (1+2+...+n - S)/(n-5)=v --> S = n(n+1)/2 - v(n-5) --> 45.1(n-5) is an integer --> n=85 only.

Now n=85 --> S=47 --> the largest possible deleted number is 37 (if the other deleted numbers are 1,2,3, and 4).

Comments: ( You must be logged in to post comments.)
  Subject Author Date
SolutionSolutionK Sengupta2007-05-20 15:02:14
re: SolutionCharlie2007-05-09 15:26:34
SolutionSolutionhoodat2007-05-09 13:32:15
SolutionsolutionCharlie2007-05-09 11:06:47
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