5+10+15+20+.....+1000
Metoda lui gauss


Răspuns :

5•(1+2+3+4+5+6+....+200)=
=5•(200•201:2)
=5•20100
=100500
(5+10+15+20+...+1000)÷5=1+2+3+...+200=(200×201)÷2=20100×5=100500