Question

calculeaza sumele s=6+11+16+21+...+101

Answer 1

s = 6+11+16+21+...+101
s = (5×1+1) +( 5×2+1) +(5×3+1) +( 5×4+1 )+...+ (5×20+1)

s = 5×(1+2+3+4 +...+20) + 1+1+1+...+1 de 20 ori

s = 5 × 20 × 21 : 2 + 1 × 20

s = 5 × 10 × 21 + 20

s = 50 × 21 + 20

s = 1050 + 20

s = 1070