Let's solve the expression:

$\frac{2}{5} + \frac{1}{4} + \frac{7}{10}$

First, find the least common denominator (LCD) of the fractions. The denominators are 5, 4, and 10. The LCD of these numbers is 20.

Next, convert each fraction to have a denominator of 20:

$\frac{2}{5} = \frac{8}{20}, \quad \frac{1}{4} = \frac{5}{20}, \quad \frac{7}{10} = \frac{14}{20}$

Now add the fractions:

$\frac{8}{20} + \frac{5}{20} + \frac{14}{20} = \frac{8 + 5 + 14}{20} = \frac{27}{20}$

The sum is:

$\frac{27}{20} = 1 \frac{7}{20}$

So, the final answer is:

$\frac{27}{20} \text{ or } 1\frac{7}{20}$

Would you like further details or have any questions? Here are some related questions you might find interesting:

1. How do you find the least common denominator?
2. How do you add fractions with different denominators?
3. What is an improper fraction and how do you convert it to a mixed number?
4. How do you subtract mixed numbers?
5. How do you multiply fractions?

Tip: When adding fractions, always ensure that they have a common denominator before performing the addition.