The sum of $2.5$ and $3.75$ is:

$2.5 + 3.75 = 6.25$

Would you like more details or have any questions?

Here are some related questions:

1. What is the sum of $4.6$ and $2.3$?
2. How would you subtract $3.75$ from $6.25$?
3. What is the result of multiplying $2.5$ by $3.75$?
4. How would you divide $3.75$ by $2.5$?
5. Can you add two fractions like $\frac{5}{2} + \frac{15}{4}$?

Tip: When adding decimals, align the numbers by their decimal points to avoid mistakes.