Bill and Sam both rode their bikes from their school to the public

Dear nemix,
Both travel a distance ---call it D. Bill took 12 minutes, and Sam took a time --- call it T. Bill traveled at speed VB and Sam traveled at speed VS.

D = RT for each person ----
For Bill: D = (VB)*12
For Sam: D = (VS)*T
Since these both equal the same distance, we can equate them.
(VB)*12 = (VS)*T

Now, statement #1 says ---- "Sam’s average speed was 80% of Bill’s." In math, VS = 0.8*VB. Plug this into the purple equation ---

(VB)*12 = [0.8*VB]*T
divide by VB
12 = 0.8*T
divide by 0.8
T = 12/0.8 = 15

It took Sam 15 minutes. Statement #1, alone and by itself, was sufficient for answering the prompt question.

As a general rule, if two people or cars travel the same distance, then their velocities are inversely proportional to the times it takes them. If, starting from one speed, you multiply by something to get the second speed --- then whatever you multiplied the speed by, you need to divide the time by that same factor.

Does all this make sense?

Mike