Question

n =1

The sum of an arithmetic series with 15 terms is 555. If the last term is 9, find the first term.

Answer 1

sum of AS = (1st term + last term)(total number of term)/2
555=(x+9)(15)/2
x=65

Answer 2

u can also apply this method:
average of terms in AP= (1st term+last term)/2
here, average= 555/15=37
last term=9, so 1st term =65