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

So we can call first number "n"

Then all five integers would be n, n+1, n+2, n+3, n+4

So sum of them would be 5n + 10 = 100

Now you can solve for n:

5n + 10 = 100

5n = 90

n = 18

Verify: 18 + 19 + 20 + 21 + 22 = 100. All good.

So answer is 18