Question

How many NAND gates are used to form AND gate?

• A. 1
• B. 2
• C. 3
• D. 4

Answer 1

Answer: (B)

Two NAND gates arranged as shown, would give an AND gate.
Here output from first NAND gate is $\overline{A\cdot B}$
This, as input, is again fed to a NAND gate, giving
$\overline{\overline{\text{ A.B. }}\cdot \overline{\text{ A.B }}}=\overline{\overline{\text{ A.B }}}+\overline{\overline{\text{ A.B }}}=A.B$