Bunuel wrote:
Carmelo and LeBron participate in a seven-person footrace on the basketball court during All-Star Weekend. If all seven contestants finish (including Charles Barkley) and there are no ties, how many different arrangements of finishes are there in which Carmelo defeats LeBron?
(A) 5040
(B) 2520
(C) 720
(D) 120
(E) 42
Kudos for a correct solution.
PRINCETON REVIEW OFFICIAL SOLUTION:Carmelo beats LeBron? Carmelo beats LeBron? No one said anything about specific results, especially not on a question that includes so many people.
Many questions on the GMAT can be overwhelming in appearance so first thing…Relax. This question looks nasty, but it’s pretty straightforward, requiring two things: the basic first calculation and then some additional work to solve the problem. It would be extremely painful to try to calculate this whole question in one fell swoop. So don’t.
Calculate out all possibilities first to get your bearings. That is, how many different arrangements, period? Since the order of arrangement again matters, this is another permutation. And since we’re placing all seven runners, this calculation is…
7 x 6 x 5 x 4 x 3 x 2 x 1, cash and prizes worth 5040 arrangements.
Now, what to do? Again, some nice deep breathing to control your nerves – relax and think. These 5040 arrangements are a comprehensive list; every possible seven-person order of finish has been counted. So, we have accounted for every time Carmelo beats LeBron AND every time LeBron beats Carmelo. Doesn’t it make sense that, for every time Carmelo beats LeBron, there is exactly one other instance in which LeBron beats Carmelo? Or more simply, doesn’t it make sense that, if these 5040 represents everything, that Carmelo beats LeBron exactly 50% of the time and vice versa?
The thought takes time. You need to have the presence to recognize that grinding your way in, around, and through this question could take roughly forever. Stepping back and recognizing that this is simply a 50/50 proposition and applying that thought to the 5040 you cranked out gives you 2520. The answer is B.
A consistent approach to certain question types can play a major role in earning more points as you build your analytic and math skills as well as your confidence. Coaches in basketball can improve your game just like a GMAT coach can do the same.