Question

Find S15 for 1 + 1.5 + 2.25 + 3.375 +...?

use the general equation Sn= T1((1-r^n)/(1-r)

Answer 1

I got: r= 1.5/1 = 1.5 ?? cause that equation I was given to find r is r= t1/t2

Answer 2

and then I put it in as S15=1((1-1.5^15)/(1-5))= 873.79..

Answer 3

but I don't think this is right.