ISRO | ISRO CS 2015 | Question 7

If half adders and full adders are implemented using gates, then for the addition of two 17 bit numbers (using minimum gates) the number of half adders and full adders required will be
(A) 0, 17
(B) 16, 1
(C) 1, 16
(D) 8, 8


Answer: (C)

Explanation: A Half Adder is used to add 2 single-bit binary numbers and a Full Adder is used to add 3 one-bit binary numbers which include two sum bits and one carry bit.
To add two 17 bit numbers using minimum gates, the least significant bits of both the numbers can be added using a half adder and for remaining 16 bits of both the numbers, full adders can be used. 1 Half Adder and 16 Full Adders will be required.
So, option (C) is correct.

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