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Official PYQ · 2015

GATE CS 2015 Set 2 Q37 — Boolean Algebra

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The number of min-terms after minimizing the following Boolean expression is _______.

[D′+AB′+A′C+AC′D+A′C′D]′[D'+AB'+A'C+AC'D+A'C'D]'
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Answer: 1

To find the number of min-terms of the given Boolean expression, let us first simplify the expression inside the complement.

Let the given expression be F=G′F = G', where:

G=D′+AB′+A′C+AC′D+A′C′DG = D' + AB' + A'C + AC'D + A'C'D

Step 1: Simplify GG

We can group the terms containing C′DC'D:

AC′D+A′C′D=(A+A′)C′D=C′DAC'D + A'C'D = (A + A')C'D = C'D

Substitute this back into the expression for GG:

G=D′+AB′+A′C+C′DG = D' + AB' + A'C + C'D

Using the distributive law on D′+C′DD' + C'D:

D′+C′D=(D′+C′)(D′+D)=D′+C′D' + C'D = (D' + C')(D' + D) = D' + C'

Now, substitute this back into GG:

G=D′+C′+AB′+A′CG = D' + C' + AB' + A'C

Using the identity X+X′Y=X+YX + X'Y = X + Y on C′+A′CC' + A'C (with X=C′X = C' and Y=A′Y = A'):

C′+A′C=C′+A′C' + A'C = C' + A'

This simplifies GG to:

G=D′+C′+A′+AB′G = D' + C' + A' + AB'

Similarly, using the identity X′+XY=X′+YX' + XY = X' + Y on A′+AB′A' + AB' (with X=AX = A and Y=B′Y = B'):

A′+AB′=A′+B′A' + AB' = A' + B'

Thus, the fully simplified expression for GG is:

G=A′+B′+C′+D′G = A' + B' + C' + D'

Step 2: Find F=G′F = G'

Using De Morgan's Law:

F=(A′+B′+C′+D′)′=A⋅B⋅C⋅DF = (A' + B' + C' + D')' = A \cdot B \cdot C \cdot D

Conclusion

The minimized expression is F=ABCDF = ABCD, which represents exactly 1 min-term (m15m_{15}).

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