3. The arithmetic sequence $\left\{a_{n}\right\}$ has a common difference of $d=2$, and $a_{1}+a_{2}+\cdots+a_{30}=100, a_{3}+a_{6}+\cdots+$ $a_{30}=$ $\qquad$
$$
\begin{array}{l}
\text { 3. } \frac{160}{3} \text {. } \\
\text { Given }\left(a_{1}+a_{2}+a_{3}\right)+\left(a_{4}+a_{5}+a_{6}\right)+\cdots+\left(a_{28}+a_{29}+a_{30}\right)=\left(3 a_{3}-3 d\right)+\left(3 a_{6}-3 d\right)+ \\
\cdots+\left(3 a_{30}-3 d\right)=100 \text {, so }\left(a_{3}+a_{6}+a_{9}+\cdots+a_{30}\right)=\frac{100}{3}+10 d=\frac{100}{3}+20=\frac{160}{3} \text {. }
\end{array}
$$
3. $\frac{160}{3}$.