Question

80+81+82+...+260 RAPIIIIIID Dau Coroana

Answer 1

80+81+82+...+260 =

(1 + 2 + 3 +...+ 260) - (1 + 2 + 3 +...+ 79) =

(260 × 261 : 2) - (79 × 80 : 2) =

130 × 261 - 79 × 40 =

33 930 - 3 160 =

30 770

Answer 2

80  +  81   +    82    +  ...  +  260 =

=80+(80+1)+(80+2) + ...  +  (80+180) =

=80×181  +  (1+2+3+ ... + 180) =

=80×181 + (180×181)/2 =

=80×181 + 90×181 =

=181×(80+90) =

=181×170=30770