A1+A2+...+A100=100

A1+(A1+D)+(A1+2D)+...+(A1+99D)=100

100A1+D(1+2+...+99)=100

A1+49,5D=1

A101+A102+...+A200=200

(A1+100D)+(A1+101D)+...+(A1+199D)=200

100A1+D(100+101+...+199)=200

A1+149,5D=2

A1+149,5D-(A1+49,5D)=2-1

100D=1

D=1/100