The first 20 even numbers are:
2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30, 32, 34, 36, 38, 40.

To find the sum of the first 20 even numbers, you can use the formula for the sum of an arithmetic sequence:

$S_n = \frac{n}{2} \times (a_1 + a_n)$

Where:

• $n$ is the number of terms (in this case, 20),
• $a_1$ is the first term (which is 2),
• $a_n$ is the last term (which is 40).

Now, plug in the values:

$S_{20} = \frac{20}{2} \times (2 + 40) = 10 \times 42 = 420$

Thus, the sum of the first 20 even numbers is 420.

Would you like further details or have any questions?

Here are 5 related questions to explore further:

1. How would you find the sum of the first 50 even numbers?
2. What is the sum of the first 20 odd numbers?
3. How can you derive a general formula for the sum of the first $n$ even numbers?
4. What is the average of the first 20 even numbers?
5. How would the sum change if we calculated it for the first 20 multiples of 3?

Tip: For any arithmetic sequence, understanding the first term, the common difference, and the number of terms will always help in finding sums easily!