How do you compare the speed of hot wheel cars and match box cars with only one variable?

My daughter is doing an experiment on hot wheel cars verses match box cars. Her question is "Is a hot wheel car faster than a match box car?" She can have only one manipulated variable (assumably the cars).|||The objective in any experiment is to keep all things "the same" EXCEPT the variable you are examining. So, for her experiment she needs to use the same track, the same time clock and - as much as possible - the same "model" cars from each brand. In other words, it's not a viable test if she compares the speed of a Hot Wheels Corvette against a Matchbox SUV. So, you should try to buy at least three (as many as you can afford and obtain) different models of cars - matching the "model / type" as closely as possible. Set up the track and time how long it takes each model to make it through the "course" (preferably just one long, downhill run. Record the times for each model's "run" and see which brand has the "fastest" cars. The only "variable" is the brand of the toy.|||yes hot wheel cars are faster than match box cars, well u may see practically