Question

Calculați suma:
1+2+3+......+80

Answer 1

80x(80+1)/2 egal 80x81/2 egal 6480/2 egal 3240

Answer 2

$\displaystyle 1+2+3+...+80= \frac{80(80+1)}{2} = \frac{80 \times 81}{2} = \frac{6480}{2} =3240$