12) B


Since 6 out of the 7 options mention ‘all values of X’ we can use X = 1 to make everything simpler. 


a =     3
       5 + X


b =   3 + X
           5


c =   3 + X
        5 + X


Substituting X = 1, 


a =     3     = 3/6 = 1/2
       5 + 1


b =   3 + 1    = 4/5
           5


c =   3 + 1    = 4/6 = 2/3
        5 + 1


The order of inequalities: a < c < b


However, option G states that the order of fractions depend on the value of X. In order to proves this wrong, we need to use a different value for X. Let us say X = 2.


a =     3     =  3/7
       5 + 2


b =   3 + 2   = 5/5 = 1
           5


c =   3 + 2    = 5/7
        5 + 2


The order still remains the same: a < c < b