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Find the number of good subsets of S - ILL 1990 IND4

Source:

September 18, 2010

symmetrycombinatorics solvedcombinatorics

Problem Statement

Let

S = \{1, 2, \ldots, 1990\}

. A

31

-element subset of

S

is called "good" if the sum of its elements is divisible by

5

. Find the number of good subsets of

S.