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Boolean Algebra and Minimization

GATE CSE 2025 Set 2 · Q31

MSQ1 markEasy

Time

Consider the following logic circuit diagram. Which is/are the CORRECT option(s) for the output function FF?

GATE CSE 2025 Set 2 Q31 diagram

Select all that applyOne or more correct

Pick every correct option

Solution

Step-by-step verified solution

Official answer: A) XY; B) X + Y + X Y; C) XY + X + X Y

Boolean Algebra and Minimization

From the given logic circuit, we trace the three inputs feeding into the final 3-input OR gate:

  1. Top Gate (NAND gate): Inputs are YY and XX, so its output is:

    XY‾\overline{XY}
  2. Middle Gate (NOT gate): Input is XX, so its output is:

    X‾\overline{X}
  3. Bottom Gate (AND gate): Inputs are XX and Y‾\overline{Y} (from the NOT gate applied to YY), so its output is:

    XY‾X\overline{Y}

Combining these through the 3-input OR gate gives the unsimplified output function FF:

F=XY‾+X‾+XY‾F = \overline{XY} + \overline{X} + X\overline{Y}

This directly matches Option (C).

Now, simplifying using De Morgan's Law and Boolean algebra:

F=(X‾+Y‾)+X‾+XY‾=X‾+Y‾+XY‾F = (\overline{X} + \overline{Y}) + \overline{X} + X\overline{Y} = \overline{X} + \overline{Y} + X\overline{Y}

This directly matches Option (B).

Further simplifying:

F=X‾+Y‾(1+X)=X‾+Y‾=XY‾F = \overline{X} + \overline{Y}(1 + X) = \overline{X} + \overline{Y} = \overline{XY}

This matches Option (A).

Option (D) is X+Y‾≠X‾+Y‾X + \overline{Y} \neq \overline{X} + \overline{Y}.

Therefore, the correct options are A, B, and C.

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This Boolean Algebra and Minimization previous year question is Q31 of the GATE CSE 2025 Set 2 paper. Find more GATE CSE PYQs on Boolean Algebra and Minimization in Digital Logic, or browse all GATE CSE PYQs.

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Boolean Algebra and Minimization in GATE CSE

Boolean Algebra and Minimization has 36 GATE CSE PYQs across 23 papers from 2011 to 2026. 5 of them are 1-mark MSQs like this one, and GATE CSE 2025 Set 2 has 3.

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GateAI solution cardGATE CSE 2025 Set 2 · Q31 · MSQ

Consider the following logic circuit diagram. Which is/are the CORRECT option(s) for the output function F?

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Independent practice explanation verified by the GateAI team. GATE is conducted by the IITs; question text follows the official paper.