a)1+99,2+98,3+97...............10+90,11+89,12+88..........20+80,21+79,22+78.............30+70,31+69,32+68...............40+60,41+59,48+52............50+50,51+49,52+48...........60+40,61+49,62+48.............70+30,71+29,72+28...............80+20,81+19,82+18...........90+10,91+9,92+8...........100+0
b) toate se impart la 4