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  1. The circuit shown in the figure has 4 boxes each described by inputs P, Q, R and outputs Y, Z with
    Y = P ⊕ Q ⊕ R, Z = RQ + P R + Q P

    The circuit is a

    2. A.
    4 bit adder giving P + Q
    B.
    4 bit subtractor giving P - Q
    C.
    4 bit subtractor giving Q - P
    D.
    4 bit adder giving P + Q + R

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    Answer : Option B

    Explanation :

    Let P = 1101 Q = 1101

    Yn = Pn ⊕ Qn ⊕ Rn

    Z = Rn Qn + Pn Rn + Qn Pn

    Constructing truth table

    So that, Rn + 1 = Zn 1 ≥ n ≥ 3

    Z4 = R5(MSB)

    Hence, output is 00010 which show that it is a 4 bit subtractor giving P - Q.

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