Question 870009
The 5th term of an arithmetic progression is three times the first term.find the sum of the first eight terms of the progression given that a quarter of the fifth term is 9

let first term be a

and common difference be d

t5 = 3a
(1/4)t5 =9
t5=36

3a=36
a=12

t5=a+4d
36=12+4d
24=4d
6=d

a=12,d=6

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

S8=(8/2)(2*12+(7*6))

=4*(14+13)
=(4*27)
=108