I need a dumbed down version of a formula for reducing/increasing the speed of a song track so that I can do the whole music video thing with alternate speeds of performance, that when readjusted are in sync with the original song track.

I've used speeding the song up twice as fast, videoing the performance and then reducing the video speed by 50% etc (which is a no-brainer even for me).
But a song that is already quite fast is impossible for people to play using this ratio even with copious amounts of methamphetamine previously ingested.

So what I'm looking for is a formula that is 100% accurate so that I can speed a song up to say 125%, then know exactly what percentage to reduce the video by.

Any help would be hugely appreciated. Aim at explaining it to a 7 year old who has suffered severe brain trauma and I'll probably be able to understand it.

Cheers.

200% = 2/1 reduce to 1/2 (=50%)
150% = 3/2 reduce to 2/3 (~66.666666666666666666667%)
125% = 5/4 reduce to 4/5 (=80%)

See the pattern?

George/

Cheers for that... just what I needed.
Love your work.