1 simplificati 2+4+6+....+140 supra 3+6+9+....+120 ; se foloseste formula lui Gauss
2+4+6+....+140=2(1+2+3+...+70)=2(70x71:2)=70x71=4970
3+6+9+....+120 =3(1+2+3+...+40)=3(40x41:2)=3x820=2460
4970/2460=497/246
2 numarul fractiilor egale cu fractia 5supra8 care au numitorul mai mic decat 63
10/16; 15/24; 20/32; 25/40; 30/48; 35/56 - 6 fractii
