Hi,
My two cents to this question
nCr means selecting “r” things out of “n”.
Remember this, if in a question total number of ways is given (the value of nCr) and how many are selected is also given (the value of r), then “n” will always a unique value.
For an example, nC2 = 10, then “n” has to be 5.
But if in a question total number of ways is given (the value of nCr) and total number of things is given (the value of n), then “r” may have more than one value.
For an example, 5Cr = 10 means “r” could be 2 or 3.
Just to add to that, remember nCr = nC(n-r).
So “r” could have more than one value.
So here in this question, n is given,
So we are finding “R”.
Statement I is sufficient:
No need to factorize this,
Just remember in a quadratic equation of the form Ax^2+Bx+ C = 0,
If B is positive and C is negative, then one root positive and one root will be negative.
So here also one value of R will be positive and one value of R will be negative.
Here negative value doesn’t make sense because we are selecting things.
So it is sufficient.
So answer has to be either A or D.
Statement II is insufficient:
It’s the first case which mentioned above,
So it could be 6C2 or 6C4
So not sufficient.
So the answer is A.
_________________
- CrackVerbal Prep Team
For more info on GMAT and MBA, follow us on @AskCrackVerbal
Register for the Free GMAT Kickstarter Course :
http://bit.ly/2DDHKHqRegister for our Personal Tutoring Course : https://www.crackverbal.com/gmat/personal-tutoring/
Join the free 4 part GMAT video training series : http://bit.ly/2DGm8tR