Evaluate (X xor Y) xor Y?
(A) All 1\’s
(B) All 0\’s
(C) X
(D) Y


Answer: (C)

Explanation: By taking a truth table, we can see the output:

X   Y     X xor Y    (X xor Y) xor Y
0   0       0             0
0   1       1             0
1   0       1             1
1   1       0             1 

Clearly the output depends on the value of X.

Alternate approach:
Through simplification of the expression, we can find the solution.

(X xor Y) xor Y
(XY\' + X\'Y) xor Y
(XY\' + X\'Y)\'Y + (XY\' + X\'Y)Y\'
(X\' + Y)(X + Y\') + XY\'
XY + XY\' = X(Y + Y\') = X 

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