What is the sum of the arithmetic series 18 sigma t-1 (5t-4) ?

The sum of the first 18 terms of the arithmetic series will be found using the formula:

Sn=n/2[2a + (n-1) d]

where

n is the number of terms

a=first term

d=common difference

from the formula above, first term is:

1-1 / (5*1-4)

=1-1 / (5-4)

=1-1/1

=0

The second term is:

2-1 / (5*2-4)

=11/6

thus the common difference is:

11/6-0=11/6

the sum of the first 18 terms will be:

S18=18/2[2*0+[18-1]*11/6]

S18=280.5