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by parallel_chase » Tue Sep 09, 2008 3:30 pm
a1+a2+....aN = 350, terms=either 7 or 77

For unit digits to be 0 the unit digit of sum of 7's and 77's should 0

therefore 3+7 = 0

we get this only when 7 is multiplied with 9

Therefore,
7*39 = 273

273+77 = 350

39+1 = 40
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