Răspuns:
Folosim formula pt suma lui Gauss: 1+2+3+...+n=n(n+1)/2
S=1+2+3+....+70=70•71/2=4970/2=2485
se aplica formula n(n+1)/2
n=70=> 70(70+1)/2 = 70×71/2 =35×71 = 2485