Question

Scrie sub forma zecimala fractia : $\frac{7 +14 +21+..........+210}{30}$.

Answer 1

$7+14+21+...+210=7*(1+2+3+4+...+30)= \frac{7*(30*31)}{2}$
$7*15*31=3255$
$\frac{3255}{30} = \frac{651}{6} = \frac{217}{3}$

Answer 2

$\frac{7+14+21+....+210}{30}= \\ \frac{7*(1+2+3+........+30)}{30}= \\ \frac{7*30*(30+1)/2}{30}= \\ \frac{210*31/2}{30}= \\ \frac{6510/2}{30}= \\ \frac{3255}{30}= \\ 108,5$