To compare how many times \( 4 \times 10^4 \) is larger than \( 2 \times 10 \), we first need to divide the two numbers:
\[ \frac{4 \times 10^4}{2 \times 10} \]
Now, simplifying this fraction:
\[ = \frac{4}{2} \cdot \frac{10^4}{10} \] \[ = 2 \cdot 10^{4-1} \] \[ = 2 \cdot 10^3 \] \[ = 2 \cdot 1000 \] \[ = 2000 \]
Thus, \( 4 \times 10^4 \) is 2000 times larger than \( 2 \times 10 \).
So the answer is \( \boxed{2000} \).