ISRO | ISRO CS 2015 | Question 8

Minimum number of multiplexers required to realize the following function,f = A’B’C + A’B’C’
Assume that inputs are available only in true form and Boolean constant 1 and 0 are available.
(A) 1
(B) 2
(C) 3
(D) 7

Answer: (B)
Explanation: The function can be simplified:

f = A’B'(C+C’) = A’B’

Since, we have to take the inputs in their true form(i.e, there is no way to get A’ or B’ directly), TWO Multiplexers will be required.

• 1st MUX will be used to get the function: AB
• 2nd MUX will be used to complement the output from the first, i.e, get A’B’

NOTE:There are other ways to solve this too.

Mux1:
I0 = 0
I1 = A
S = B
Output = 0 + AB = AB

Mux2:
I0 = 1
I1 = 0
S = AB (output from Mux1)
Output = (AB)’ = A’B’ (which is the desired output)

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