Question 9232 – GATE 2007

How many 3-to-8 line decoders with an enable input are needed to construct a 6-to-64 line decoder without using any other logic gates?

Correct Answer: C

Question 8 Explanation:

Each 3-to-8 lines decoder has 8 output lines.
So, we can say that
8 lines covered by —– 1 decoder
1 line covered by —– 1/8 decoder
64 lines covered by —– 64/8 = 8 decoders
8 lines covered by —– 8/8 = 1 decoder
Hence total no. of decoder needed is,
8 + 1 = 9 decoders.