Say I am asked questions in MCQ like "The number of two-input NAND gates required to produce the two input OR function is"?
Manually solving this(paper is not given in exam neither time is there).
Any guidance?

 

Hint:
For negative logic (a low voltage being a logic 1) the functions of a NOR and NAND gate are interchanged

 

Any guidance?

As this is in homework help, you need to show your attempt so we can see what guidance you need.

Do you know De Morgan's Theorem?