For any numbers a and b, a · b = a + b - ab. If a · b = 0, which of the following CANNOT be a value of b? (A) 2 (B) 1 (C) 0 (D) -1 (E) 2







a · b = a + b - ab
0 = a + b - ab
so a = b/(b-1)
so b cannot equal 1



If 1=(x+y)/yx, then y =
(A)x/(x-1)
(B) x/(x+1)
(C) (x-1)/x
(D) (x+1)/x
(E) x



1=(x+y)/yx
yx=x+y
yx-y=x
y(x-1)=x
y=x/(x-1)
Ans : A