There is a race. Participants A and B.
A finishes in 29 minutes
B finishes in 35 minutes

A is 6 minutes faster than B.
B is 6 minutes slower than B.

Is A 17% or 21% faster than B?
Is B 17% or 21% slower than A?

Title says it all, darn percentages :)

If someone needs more than 20 minutes to finish a race, tell both of them to get their fat rear ends out of the local Burger King and into a gym! :)