1. **State the problem:** There are 400 students in Maureen's high school, and 90% of them are taking Spanish. We need to find how many students are taking Spanish. 2. **Formula used:** To find a percentage of a number, use the formula: $$\text{Part} = \frac{\text{Percent}}{100} \times \text{Whole}$$ 3. **Apply the formula:** Here, the percent is 90 and the whole is 400. $$\text{Students taking Spanish} = \frac{90}{100} \times 400$$ 4. **Calculate:** $$= 0.9 \times 400 = 360$$ 5. **Interpretation:** So, 360 students are taking Spanish. **Final answer:** 360 students are taking Spanish.