We often refer to this type of question as a "wacky symbol" or "symbolism" question; it's really a function question in disguise. For example, we could have restated this question as:JeetGulia wrote:16. 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) -3/2
Please help....
If f(a,b) = a + b - ab, and f(a,b) = 0, which of the following cannot be the value of b?
We start by applying a fundamental rule of math: no matter how weird things look, the same basic rules apply. We know that:
a · b = a + b - ab
and
a · b = 0
So, we can substitute in for the left side of the original equation to get:
0 = a + b - ab
ab = a + b
Rather than attacking this equation in the abstract, let's plug in the choices:
(A) 2
2a = a + 2
a = 2... works
(B) 1
a = a + 1
0 = 1... IMPOSSIBLE... therefore, (B) is the correct choice.
