Question

Rezultatul calculului 5+10+15+...+40 este egal cu...

Answer 1

$\displaystyle 5+10+15+...+40=5(1+2+3+...+8)=5 \times \frac{8(8+1)}{2} = \\ \\ =5 \times \frac{8 \times 9}{2} =5 \times \frac{72}{2}=5 \times 36=180$

Answer 2

5+10+15+...+40=
5*(1+2+3+...+8)=
5 * $\frac{8*(8+1)}{2}$=

5* $\frac{8*9}{2}$

5* 4 * 9
20*9
180