1. **State the problem:** There are 20 rows with 25 seats each, and 450 people attend a movie. We want to find the minimum number of rows that must have the same number of people seated. 2. **Identify the principle:** This is a classic application of the Pigeonhole Principle, which states that if $n$ items are put into $k$ containers, then at least one container must contain at least $\lceil \frac{n}{k} \rceil$ items. 3. **Apply the principle:** Here, the "items" are the 450 people, and the "containers" are the 20 rows. 4. **Calculate:** $$\text{Minimum number of people per row} = \left\lceil \frac{450}{20} \right\rceil = \left\lceil 22.5 \right\rceil = 23$$ 5. **Interpretation:** At least one row must have at least 23 people seated. 6. **Answer:** Therefore, the minimum number of people in at least one row is 23, meaning at least one row will be occupied by 23 or more people. 7. **Additional note:** Since the question asks how many rows at least will be occupied by the same number of people, by the Pigeonhole Principle, at least $\boxed{23}$ people will be seated in at least one row.