Question

Every 10 seconds a pendulum completes 2 cycles. what are the period and frequency of this pendulum

Answer 1

period 5 sec = 1 cycle
f = 1/period
.2

Answer 2

If it completes 2 cycles in 10 seconds, then each cycle
takes 5 seconds. That's the period.

Frequency = 1 / period = 1 / 5 sec = 0.2 per sec = 0.2 Hz.