Difference between revisions of "2007 iTest Problems/Problem 6"
(New page: ==Problem== Find the units digit of the sum <cmath>\sum_{i=1}^{100}(i!)^{2}</cmath> <math>\mathrm{(A)}\,0\quad\mathrm{(B)}\,1\quad\mathrm{(C)}\,3\quad\mathrm{(D)}\,5\quad\mathrm{(E)}\,7\...) |
(No difference)
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Revision as of 11:04, 16 December 2007
Problem
Find the units digit of the sum
Solution
If i is less than 5, then has a positive units digit, if , then has a units digit of 0, as does . So we only need to worry about i=1-4.
, which has a units digit of 7