To simplify the expression \( A = \left( \frac{1}{3} - \frac{3}{10} \right) : \frac{3}{5} + \left( \frac{2}{3} - \frac{7}{10} \right) : \frac{3}{5} \), we will follow these steps:

1. **Calculate each parenthesis separately**.
2. **Convert each division to multiplication by the reciprocal**.

Let's start with the first term:

\[
\frac{1}{3} - \frac{3}{10}
\]

To subtract these fractions, we need a common denominator. The least common multiple of 3 and 10 is 30.

Convert \(\frac{1}{3}\) and \(\frac{3}{10}\) to have a denominator of 30:

\[
\frac{1}{3} = \frac{10}{30}, \quad \frac{3}{10} = \frac{9}{30}
\]

Thus,

\[
\frac{1}{3} - \frac{3}{10} = \frac{10}{30} - \frac{9}{30} = \frac{1}{30}
\]

Now we calculate the first term of \( A \):

\[
\left( \frac{1}{3} - \frac{3}{10} \right) : \frac{3}{5} = \frac{1}{30} : \frac{3}{5} = \frac{1}{30} \cdot \frac{5}{3} = \frac{5}{90} = \frac{1}{18}
\]

Now for the second term:

\[
\frac{2}{3} - \frac{7}{10}
\]

Again, we find a common denominator. The least common multiple of 3 and 10 is again 30.

Convert \(\frac{2}{3}\) and \(\frac{7}{10}\) to have a denominator of 30:

\[
\frac{2}{3} = \frac{20}{30}, \quad \frac{7}{10} = \frac{21}{30}
\]

Thus,

\[
\frac{2}{3} - \frac{7}{10} = \frac{20}{30} - \frac{21}{30} = \frac{-1}{30}
\]

Now we calculate the second term of \( A \):

\[
\left( \frac{2}{3} - \frac{7}{10} \right) : \frac{3}{5} = \frac{-1}{30} : \frac{3}{5} = \frac{-1}{30} \cdot \frac{5}{3} = \frac{-5}{90} = \frac{-1}{18}
\]

Now combine the two parts of \( A \):

\[
A = \frac{1}{18} + \left( \frac{-1}{18} \right) = 0
\]

Thus the final answer is:

\[
\boxed{0}
\]