I have to stop people from doing this in presentations all the time lol. Just say "Runtime decreased from 117s to 34". It is really easy to mentally compare two numbers; it is much harder to start with "Runtime decreased by 71% to 34s" and find the old value. Equally brief, never any ambiguity, easier on the mind, and no weird explosions as you approach zero.

I'd wager it's the first (51.1%). Mostly because I simply cannot imagine that nearly 70% of kids in 2005 enjoyed reading. That seems too high. Based on..? My vibes.