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2014-11-11T15:32:38+02:00
A)4(1+2+3+............+30)
4(30+1)x30:2
4x 31 x 15=124x15
                =1860
b)2(1+2+3+...+35)
2(35+1)x35:2
2x36x35:2=
2x35+18=70+18
  =88