Period and frequency are the same fact read in opposite directions: $T = \dfrac{1}{f}$ — read aloud: T equals one over f. Five cycles each second means each cycle gets a fifth of a second; nothing deeper hides in there. Flip it and $f = \dfrac{1}{T}$: the same seesaw, ridden from the other end.

The formula is its own inverse — flipping is the ENTIRE job — and that is precisely why it catches people. It looks too small to matter, so the number walks through untouched: 2 Hz becomes “2 s”, and the exam collects. A rate is not a time until you flip it. Small formula, full marks either way.