设公差为da2+a5=2a1+5d=2×(1/3)+5d=4d=2/3an=a1+(n-1)d1/3 +(2/3)(n-1)=33(2n-1)/3=332n=100n=50
设a1+x=a2则a1+x+a1+x+x+x+x=42a1+4x=4又a1=1\3x=5\6a1+nx=331\3+n*5\6=33n=198\5
