system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why does watching a video at 1.25 speed decrease the time by 20%? And 1.5 speed decreases it by 33%?

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.
gpt
If you went 2.00 times faster, would you expect to get there instantly? No, instead, it's half the time. When you go X times faster, you reduce the time to 1/X. So 2 times faster makes the time 1/2 what it was. 5 times faster, you'd get there in 1/5th the time. 1.25 times faster can be expressed as 5/4 times faster, and you get there in 4/5th the time, or 80%.