1. **Problem statement:** We have the practice times (in minutes) of four students: An, Bảo, Hưng, and Trí. 2. **Part a:** Create a data table of the practice times. | Học sinh | An | Bảo | Hưng | Trí | |----------|----|-----|-------|-----| | Thời gian (phút) | 70 | 60 | 50 | 80 | 3. **Part b:** Calculate the ratio of Trí's practice time to the total practice time of An, Bảo, and Hưng. 4. **Formula:** $$\text{Ratio} = \frac{\text{Trí's time}}{\text{An's time} + \text{Bảo's time} + \text{Hưng's time}}$$ 5. **Calculation:** $$\text{Sum of An, Bảo, Hưng} = 70 + 60 + 50 = 180$$ $$\text{Ratio} = \frac{80}{180} = \frac{8}{18} = \frac{4}{9} \approx 0.4444$$ 6. **Interpretation:** Trí's practice time is approximately 44.44% of the total practice time of An, Bảo, and Hưng. **Final answer:** $$\boxed{\frac{4}{9} \text{ or approximately } 0.4444}$$