a. 1/100 + 2/100 + ...+ 99 /100=
=(1+2+..+99)/100=(99×100/2)/100=99/2=49,5
b. 2/501 + 4/501 + ... +1000/501=
=(2+4+...+1000)/501=2(1+2+...+500)/501=(2×500×501/2)/501=500
c. 1/101 + 3 pe 101 + .... +199/101=
=(1+3+...+199)/101=[(1+2+3+...+198+199)-(2+4+...+198)]/101=
=[199*200/2-2(1+2+...+99)]/101=
=[19900-(2×99×100/2)]/101=
=(19900-9900)/101=
=10000/101=99,(0099)