To compare the two numbers \( 5 \times 10^{-11} \) and \( 3 \times 10^{-11} \), we can directly compare the coefficients since they are both multiplied by the same power of ten.
Here are the numbers:
- \( 5 \times 10^{-11} \)
- \( 3 \times 10^{-11} \)
Since \( 5 \) is greater than \( 3 \), we have:
\[ 5 \times 10^{-11} > 3 \times 10^{-11} \]
So the symbol that makes the statement true is \( > \).
Thus, the complete statement is:
\( 5 \times 10^{-11} > 3 \times 10^{-11} \)