Question

S=1+2+3.......+n Aflati n stiind ca este 5% din S

Answer 1

.................................

Answer 2

5%=5/100=1/20
atunci
n=(1/20)*n(n+1)/2
simplificam cu n≠0
1=(n+1)/40
n+1=40
n=39
 as simple as that!