A2. The first term of an arithmetic sequence is $\frac{1}{3}$, and the third term is $\frac{1}{5}$. What is the second term of this sequence?
(A) $\frac{1}{4}$
(B) $\frac{4}{15}$
(C) $\frac{5}{24}$
(D) $\frac{7}{30}$
(E) $\frac{2}{9}$
A2. The second term of the arithmetic sequence is $a_{2}=\frac{1}{2}\left(a_{1}+a_{3}\right)=\frac{1}{2}\left(\frac{1}{3}+\frac{1}{5}\right)=\frac{4}{15}$.