Question

1+2+3+.............+124=?

Answer 1

   

$\displaystyle\\</p><p>1+2+3+...+124=\frac{124(124+1)}{2}=62\times125=\boxed{\bf 7750}$

Answer 2

n(n+1):2

unde n este ultimul termen adica 124

deci vine 124*125:2=15500:2=7750