Problem 64

First, calculate the difference between 500,000 and 400,000:
$$500,000 - 400,000 = 100,000$$

Then, divide the difference by 50 to find the number of times:
$$\frac{100,000}{50} = 2,000 \text{ times}$$

Therefore, the answer is: $\boxed{2000}$.

Starting from 400,000 and counting by increments of 50, which means each time you count, the number increases by 50 until it reaches 500,000. By calculating $500,000 - 400,000 = 100,000$ and then dividing $100,000$ by $50$, we find it takes $2,000$ times; this is how the problem is solved.

This question is prone to errors. It should be clear that counting starts from 400,000, meaning that 400,050 is counted as the first time.