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To get an output Y=1 from the circuit shown, the input must be

Asked in NEET 2010 · Gate combinations and truth tables

Figure: Gate combinations and truth tables
Answer: (3) A=1, B=0, C=1

Step-by-step solution

Idea: reduce the two gates to one expression before testing any of the four sets.

The OR gate takes A and B and gives A+B.

The AND gate takes that signal together with C, so Y=(A+B)· C.

Y=1 needs both factors high: C=1, and at least one of A and B equal to 1.

A=1, B=0, C=1 gives (1+0)·1=1.

Each of the other three sets fails one of the two conditions, so this is the only one that works.

Why the other options are wrong

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