The pendulum has made 100 oscillations in 25 determine the period and frequency of the pendulum’s oscillations.

The oscillation period is such a period of time during which the body returns to the same point from which it began its movement.
T = t / n, where n is the number of oscillations, t is the time during which the body made these oscillations.
T = t / n = 25/100 = 0.4 s.
The oscillation period depends on the frequency according to the law:
T = 1 / ν
Let us express the frequency from this expression:
ν = 1 / T = 1 / 0.4 = 2.5 Hz.
Answer: the oscillation period is 0.4 s, and the frequency is 2.5 Hz.