Difference between revisions of "2003 AIME I Problems/Problem 3"

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== Solution ==
 
== Solution ==
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Order the numbers in the set from greatest to least to reduce error: <math>\{34, 21, 13, 8, 5, 3, 2, 1\}.</math>
 
Each [[element]] of the [[set]] will appear in <math>7</math> two-element [[subset]]s, once with each other number.
 
Each [[element]] of the [[set]] will appear in <math>7</math> two-element [[subset]]s, once with each other number.
  

Revision as of 19:28, 18 February 2012

Problem

Let the set $\mathcal{S} = \{8, 5, 1, 13, 34, 3, 21, 2\}.$ Susan makes a list as follows: for each two-element subset of $\mathcal{S},$ she writes on her list the greater of the set's two elements. Find the sum of the numbers on the list.

Solution

Order the numbers in the set from greatest to least to reduce error: $\{34, 21, 13, 8, 5, 3, 2, 1\}.$ Each element of the set will appear in $7$ two-element subsets, once with each other number.

  • $34$ will be the greater number in $7$ subsets.
  • $21$ will be the greater number in $6$ subsets.
  • $13$ will be the greater number in $5$ subsets.
  • $8$ will be the greater number in $4$ subsets.
  • $5$ will be the greater number in $3$ subsets.
  • $3$ will be the greater number in $2$ subsets.
  • $2$ will be the greater number in $1$ subsets.
  • $1$ will be the greater number in $0$ subsets.

Therefore the desired sum is $34\cdot7+21\cdot6+13\cdot5+8\cdot4+5\cdot3+3 \cdot2+2\cdot1+1\cdot0=\boxed{484}$.

See also

2003 AIME I (ProblemsAnswer KeyResources)
Preceded by
Problem 2
Followed by
Problem 4
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
All AIME Problems and Solutions
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