Răspuns:
2 × ( 1 + 2 + 3 +...... + 50)
2× ( 50 × 51 ÷2 )
2× (25 x 51)
2 x 1275
2550
2x(1+2+3+...+50)=
2x50x(50+1)/2=
100x51/2=
50x51=2550.
