1.已知等差数列{an}的公差为1,且a1+a2+a3+……+a99=99,则a3+a6+…+a99的值为（ ）

a1+a2+a3+.+a99=99
--->99a1+99*98d/2=99
--->a1+49d=1
a3+a6+a9+.+a99
=33a3+33*32*3d/2
=33(a3+48d)
=33(a1+50d)=33(1+d)=33*2=66
a2=a1+d
a4=a3+d
.
a100=a99+d
a2+a4+...a100=a1+a3+...+a99+50d=60+25=85
S100=60+85=145
a1+an=a5+an-4 (n-4)为下标
187/n=(187-26-110)/(n-8)
n=11