Question

Calculati sumel:s=4+7+10+....+91 b)s=6+11+16+21+.....101

Answer 1

s=4+7+10+....+91
s = 3×1+1+3×2+1+3×3+1+...+3×30+1
s = 3×(1+2+3+...+30) + 1+1+1+...+1 de 30 ori
S = 3×30×31:2 + 1×30
S = 3×15×31 + 30
S = 1 395 + 30
S = 1 425

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 = 1 050 + 20
s = 1 070