To find the sum of this arithmetic series, we can use the formula for the sum of the first n terms of an arithmetic series:

S = n/2 * (first term + last term)

In this case, the first term is 1, the last term is 1100, and the common difference is 5.

So, the number of terms in the series is:

n = (last term - first term) / common difference + 1
n = (1100 - 1) / 5 + 1
n = 220

Now we can plug these values into the formula:

S = 220/2 * (1 + 1100)
S = 110 * 1101
S = 121,110

Therefore, the sum of the series 1+5+10+...+1100 is 121,110.