Question

The period of a wave is found to be 50 seconds. What is the frequency of the wave?

Answer 1

If you remember this one rule, then you can always convert
in either direction between frequency and period.

           (Frequency) times (Period)  =  1 .

So Frequency = 1 / period

                         =  1 / (50 seconds)

                         =  (1/50) per second

                         =   0.02 per second

                         =  0.02 Hertz  

Answer 2

The answer is this.
 1/50 = 0.02 Hz