Question

Calculati:8+16+24+32+.....+4000=

Answer 1

8+16+24+32+.....+4000=
8x(1+2+3+4+......+500)=
8x500x(500+1):2=
8x500x501:2=
8x50x501=
400x501=
200001

Answer 2

$\displaystyle 8+16+24+32+...+4000=8(1+2+3+...+500)= \\ \\ =8 \times \frac{500(500+1)}{2} =8 \times \frac{500 \times 501}{2} =8 \times \frac{250500}{2} = \\ \\ =8 \times 125250=1002000$