Question

Calculati urmatoarele sume: a) 1+2+3+.....+80=
b) 2+4+6+......+100
C) 1+3+5+.......+99

E de cls a 5-a,va roooog,ajutati-ma

Answer 1

a) (80 X 81):2 = 40 X 81
                       =3 240
b)100 : 2 = 50
    2 X [50 X (50  : 2)+25]
    2 X (50 X 25 +25)
    2 X (1250 + 25)
    2 X 1275
    2550
   c)99 -1 = 98
      98 : 2 = 49
      2 x [98 x (98 : 2) +49]
      2 X (98 X 49 :2) +49
      2 X (4802 :2) + 49
      2 X 4851
      9702
a) 3240, b)2550, c) 9702.
Sper ca te-am ajutat !!!
Coronita te rog!!!