1. **State the problem:** There are 30 students in the class, and two-thirds of them are girls. We need to find how many girls are in the class. 2. **Formula used:** To find a fraction of a quantity, multiply the total quantity by the fraction. 3. **Apply the formula:** Number of girls = $\frac{2}{3} \times 30$ 4. **Calculate:** $$\frac{2}{3} \times 30 = \frac{2 \times 30}{3} = \frac{60}{3}$$ 5. **Simplify the fraction:** $$\frac{\cancel{60}}{\cancel{3}} = 20$$ 6. **Interpretation:** There are 20 girls in the class. **Final answer:** 20 girls