If term 3=15/16, term6= 5/18 and the last term is 40/729, find the number of terms in the sequence if the sequence is geometric

Answer 1

there are 3 ratios between 15/16 and 5/18 ... (15/16) * r^3 = 5/18
... r = [(5/18) / (15/16)]^(1/3)

to find the number of terms (n) ... (15/16) * r^(n-3) = 40/729
... n-3 = log[(40/729) / (15/16)] / log(r)