Thanks aliag916 and Tim. I went through the same confusion and it got resolved after reading this post. So Tim, since the order is not important, we can use 10C5 right? Coz that's what I've used and it comes up to be same as aliag916's answer. Just needed confirmation on the use of 10C5 here. Cheers...

If x=(9b-3ab)/((3/a)-(a/3)) , what is x (1) 9ab/(3+a) = 18/5 (2) b = 1 Shoudn't the answer be (E) here. Acc. to the explanation, you simplify the main expression to get: 9ab(3-a)/((3-a)(3+a)) and then you cancel (3-a) !! But can we really cancel (3-a)? We don't know if "a" is not equal to ...