Question

Calculati 5+10+15+......+995

Answer 1

5 + 10 + 15 + ..... + 995 =?
Termenii au forma de 5 x K + 5 
5 = 5 x 0 +5
10 = 5 x 1 + 5 
15 = 5 x 2 + 5 
......................
995 = 5 x ? = 5 
995 - 5 = 990 
990 : 5 = 198 
995 = 5 x 198 + 5 
S = 5 x ( 0 + 1 + 2 + 3 +....... + 198 ) : 2 + 199 x 5 = ?
S = 5 x 198 x 199 : 2  + 995 = ?
S = 5 x 99 x 199 + 995 = ?
S = 5 x 19701 + 995 = ? 
S = 98505 + 995 = ?
S = 99500