Question

Answer 1

33+35+37+39+41+43+45+47=(33+47)+(35+45)+(37+43)+(39+41)=80+80+80+80=320

14+15+16+17+18+19+20+21+22+23+24+25+26=(14+26)+(15+25)+(16+24)+(17+23)+(18+22)+(19+21)+20=40+40+40+40+40+40+20=40x6+20=240+20=260

Answer 2

a: Số số hạng là:

(47-33):2+1=8(số)

Tổng là:

\(\dfrac{\left(47+33\right)\cdot8}{2}=80\cdot4=320\)