Turns ratio:

The turns ratio in the transformer is ratio of the number of turns in primary, T_pri, to the number of turns in secondary, T_sec. This ratio can be given by Tpri:T_sec or T_pri/T_sec.

In the transformer with excellent primary to secondary coupling, following relationship always holds:

E_pri/E_sec  = T_pri/T_sec

That is, primary to secondary voltage ratio is equal to the primary to secondary turns ratio shown in the figure given below.

Figure--   Primary and secondary turns and voltages in a transformer.

Problem: 

A transformer has a primary to secondary turns to ratio of exactly 9:1. The voltage at primary is 117 V. What is voltage at secondary?

This is step down transformer. Simply plug in numbers in the above equation and explain for Esec:

E_pri/E_sec = T_pri/T_sec

117/E_sec = 9/1= 9

1/E_sec = 9/117

E_sec = 117/9 =13 V