vinaymimani wrote:

If\({n}_{C}_{r}\) gives a prime value,is \(r=n-1\)?

I. n is prime

II. r is not prime

Question created by me,constructive feedback welcome.Kudos to the first correct answer!

Dear

vinaymimaniZarrolou already gave a brilliant solution. I'll just add --- this question doesn't strike me as particularly GMAT-like. Yes, it's a hard question, but I don't know --- it seems very abstractly mathematical and from what I can tell, the most straightforward solutions are simply plug-in of various single digit numbers, as

Zarrolou did. On the most challenging math problems, it strikes me that the GMAT creates more elegant problems. It's easier to write a hard problem, but it's more difficult to write an elegant problem. That's just my 2¢

Mike

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Mike McGarry

Magoosh Test Prep