To subtract \( 1.7 \times 10^8 \) from \( 405,000,000 \), we first convert \( 405,000,000 \) to scientific notation.
\[ 405,000,000 = 4.05 \times 10^8 \]
Now, we can perform the subtraction:
\[ 4.05 \times 10^8 - 1.7 \times 10^8 = (4.05 - 1.7) \times 10^8 \]
Calculating \( 4.05 - 1.7 \):
\[ 4.05 - 1.7 = 2.35 \]
Thus, we have:
\[ 2.35 \times 10^8 \]
So, the final answer is:
\[ \boxed{2.35 \times 10^8} \]