floor(random(5)+1 will result in 1,2,3,4,5
Better yet, skip the random and use
choose(1,2,3,4,5) = 1
this means 20% chance (or 1 out of 5 chance) of choosing 1st car, then do the same for other cars
choose(1,2,3,4,5) = 2
choose(1,2,3,4,5) = 3
choose(1,2,3,4,5) = 4
choose(1,2,3,4,5) = 5