Question

5+10+15+...+95=? vă rog cat mai repede​

Answer 1

Dam factor comun 5.

5·(1+2+3+....+19)=

Acum ne folosim de suma lui Gauss:

Acum ne folosim de suma lui Gauss:1+2+3+...+n=n(n+1):2

5·(19·20:2)=

=5·(19·10)=

=5·190

=950

Answer 2

5+10+15+....+95

19 termeni

19×(95+5):2=19×100:2=950