I assume you're sayng that all the cars differ in at least one aspect......so...there are 24 "different" cars, thusly:
(H, W,2) (V, W,2) (F, W, 2) (C, W,2)
(H, W,4) (V, W,4) (F, W, 4) (C, W,4)
(H, R, 2) (V, R,2) (F, R, 2) (C, R, 2)
(H, R, 4) (V, R 4) (F, R, 4) (C, R, 4)
Notice that there are 4 ways to pair the Hondas with a "different" Volvo, "different" Ford or "different" Cadillac. So, 4 + 4 + 4 = 12
And there are 4 ways to pair the Volvos wth a "different" Ford or "different' Cadillac. {We've already paired each with a "different" Honda.} So 4 + 4 = 8
And since we've already paired the Fords with a "different" Honda or Volvo, we have 4 ways that we can pair them with a "different" Cadillac.
So there are 12 + 8 + 4 = 24 "different" pairings
And the total number of possible pairs made by selecting any 2 cars from 24 = C(24,2) = 276
So 24 / 276 = 2/23 = about an 8.7% chance of pairing two "different" cars......
