ISRO | ISRO CS 2011 | Question 6

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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