Question

how many two input NAND gates are required to perform the action of a two input OR gate?

Answer 1

We can use 3 NAND gates to perform the action of an OR gate.

We first use 2 NAND gates, and their outputs are connected to the third NAND gate, which then produces the same result as an OR gate.

If X is the initial input in the first NAND gate, we get
(X.X)`
= X`

If Y is the initial input in the second NAND gate, we get
(Y.Y)`
= Y`

When we connect these two outputs to the input of the third NAND gate, we get
(X` . Y`)`
= (X`)` + (Y`)`
= X + Y
which is an OR gate.

Answer 2

correct Answer is : Three NAND gates

Explanation :

 ⇒We can use three NAND gates to perform the action of an two input OR gate.

⇒NAND gate is called as Universal gate.

⇒See the attachment for the figure:

⇒First two NAND gates are used and the ouput is given to Third NAND gate which results in OR gate .
   
                                                         ____  
                                                           _  _        =   =    
⇒The Boolean Expression is :  Y= A.B   =  A +B = A+B read as Y= A or B