The sum of $1 + 2$ is:

$1 + 2 = 3$

Would you like more details or have any questions?

Here are five related questions:

1. What is $3 + 4$?
2. How do you add two numbers with decimals, like $1.5 + 2.3$?
3. What is the sum of $1 + 2 + 3 + 4$?
4. How can you add two negative numbers, such as $-1 + -2$?
5. Can you explain the difference between addition and multiplication?

Tip: Always remember to align decimal points when adding decimal numbers.