Our favorite maths expert has a video where he "worked out" how much the original apollo "jump salute" clip was "slowed down." He admitted that increasing a presumably half-speed video by 50% only increased it to 75% it's "original" speed, yet made the mistake again.

He increased the original video by 150%, and then "worked out" how much he needed to slow it down back to the original. It took him some fancy video software to work out he needed to slow it by 67%, or 2/3. So, whilst the "original speed" was 150%, or 3/2 (a number he pulled out of his ass) he basically proved that 3/2 * 2/3 = 1. That's it. He didn't prove anything other than that.