1. **State the problem:** Diana initially has 12 birds, 8 of which are green. She buys 9 more green birds. We need to find the fraction of green birds out of the total birds now. 2. **Identify the formula:** The fraction of green birds is given by $$\frac{\text{number of green birds}}{\text{total number of birds}}$$. 3. **Calculate the new number of green birds:** $$8 + 9 = 17$$ 4. **Calculate the new total number of birds:** $$12 + 9 = 21$$ 5. **Form the fraction:** $$\frac{17}{21}$$ 6. **Simplify the fraction if possible:** The greatest common divisor of 17 and 21 is 1, so the fraction is already in simplest form. **Final answer:** The fraction of Diana's birds that are green now is $$\frac{17}{21}$$.