Răspunsuri

2014-10-13T12:32:22+03:00
1+2+3+4+5.......+99 = 99 * 100 / 2 = 99 * 50 = 4950

1+3+6+9........+99 = 
Calculam numarul de termeni:
[(99 - 1) / 2] + 1 = (98 / 2) + 1 = 49 + 1 = 50
1+3+6+9........+99 = 50 * (99 + 1) / 2 = 50 * 100 / 2 = 50 * 50 = 2500