Why does watching a video at 1.25 speed decrease the time by 20%? And 1.5 speed decreases it by 33%?

Question

I guess this reveals how fucking dumb I am. I can’t get the math to make sense in my head. If you watch at 1.25 speed, logically (or illogically I guess) I assume that this makes the video 1/4 shorter, but that isn’t correct.

In short, could someone reexplain how fractions and decimals work? Lol

Edit: thank you all, I understand now. You helped me reorient my thinking.

In: 8653

Answer 1

5/4 speed = 4/5 time taken, i.e. shorter by 1/5

3/2 speed = 2/3 time taken, i.e. shorter by 1/3