1. **State the problem:** We are given that $\frac{2}{7}$ of the students have a younger sibling, and 25 students do not have a younger sibling. We need to find the total number of students in the class. 2. **Define variables:** Let the total number of students be $x$. 3. **Express the number of students with and without younger siblings:** - Students with younger siblings: $\frac{2}{7}x$ - Students without younger siblings: $x - \frac{2}{7}x$ 4. **Simplify the number of students without younger siblings:** $$x - \frac{2}{7}x = \frac{7}{7}x - \frac{2}{7}x = \frac{5}{7}x$$ 5. **Set up the equation using the given number of students without younger siblings:** $$\frac{5}{7}x = 25$$ 6. **Solve for $x$:** Multiply both sides by 7: $$7 \times \frac{5}{7}x = 7 \times 25$$ $$\cancel{7} \times \frac{5}{\cancel{7}}x = 175$$ $$5x = 175$$ Divide both sides by 5: $$\frac{5x}{5} = \frac{175}{5}$$ $$\cancel{5}x = 35$$ $$x = 35$$ 7. **Answer:** The total number of students in the class is **35**.