Tim and Rick both can run at speed vr and walk at speed vw, with vr>vw. They set off together on a journey of distance D. Rick walks half of the distance and runs the other half. Tim walks half of the time and runs the other half.

Question:

How long does it take Rick to cover the distance D?

The time, , Rick takes to cover the distance D is;

Explanation:

Here we have the running speed of Rick = and

The walking speed of Rick =

Therefore, since Rick walks half of the distance and runs the other half, we have

Where

Distance for walking = D/2 and distance for running = D/2

Rick's time in running is

and time in walking is

Total time is given by

there is no correct list among the choices you've provided.

the list might look something like this:

-- baby human

-- piccolo

-- flute

-- soprano singer

-- trumpet

-- tenor singer

-- trombone

-- baritone singer

-- baritone horn

-- bass singer

-- tuba

since i had to make up the list myself, i made it easy on myself, and i didn't try to shuffle the string instruments and woodwinds into it too.