1
Question
A bank has 3 locks with 1 key for each lock. Each key is owned by a different person. In order to open the vault atleast two people must insert their keys into the assigned locks. All the keys are not inserted at the same time. If the system is to be designed with only two input NAND gates then the number of NAND gates required are _____
- 6
- 6
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Solution
The correct option is A 6
Let the 3 locks are A,B,C
Key not insert treated as logic 0.
Key inserted treated as logic 1.
A
B
C
Y
0
0
0
0
1
1
1
1
0
0
1
1
0
0
1
1
0
1
0
1
0
1
0
1
0
0
0
1
0
1
1
X
The expression for Y is similar to carry in full adder circuit.
So, number of two input NAND gates required are 6.
Let the 3 locks are A,B,C
Key not insert treated as logic 0.
Key inserted treated as logic 1.
| A | B | C | Y |
| 0 0 0 0 1 1 1 1 |
0 0 1 1 0 0 1 1 |
0 1 0 1 0 1 0 1 |
0 0 0 1 0 1 1 X |
The expression for Y is similar to carry in full adder circuit.
So, number of two input NAND gates required are 6.
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