a) 3/505 ·(1+2+3+......+100) = 3/505 ·100·101/2 =30
c) 1/101 +10/(101·91) + 10/(91·81) + 10/(81·71) +.........10/(21·11) =
= 1/101 + 1/91 - 1/101 +1/81 - 1/91 +1/71 - 1/81+........+ 1/11 - 1/21 =
= 1/11
b) scrie corect enuntul ! ce inseamna 1 langa 1/3 ?