Question

The sum of 5 consecutive even numbers is 100.
What is the first number in this sequence?

Answer 1

Good God, do you REALLY need help with this? And you're in college?

The sum of 5 consequential even numbers add to 100. Let's use N as the first number. So you have
N + (N+2) + (N+4) + (N+6) + (N+8) = 100

Now solve for N. 
5N + 2 + 4 + 6 + 8 = 100
5N + 20 = 100
5N = 80
N = 16

Answer 2

Consecutive numbers are 1 apart.
Consecutive even numbers are 2 apart.
If x is the smallest of 5 consecutive even numbers, then the next 4 consecutive even numbers are x + 2, x + 4, x + 6, and x + 8.

Add all 5 numbers and set equal to 100.
Then solve for x, the smallest of the 5 numbers.

x + x + 2 + x + 4 + x + 6 + x + 8 = 100

5x + 20 = 100

5x = 80

x = 16

The first number is 16.