Question

What distinguishes the look-ahead-carry adder?

(a) It is slower than the ripple-carry adder

(b) It is easier to implement logically than a full adder

(c) It is faster than a ripple-carry adder

(d) It requires advance knowledge of the final answer

The question was asked during an online exam.

This interesting question is from 4-Bit Parallel Adder/Subtractor in chapter Arithmetic Circuits of Digital Circuits

Answer 1

Correct answer is (c) It is faster than a ripple-carry adder

The best I can explain: It is faster than ripple carry adder as it reduces the propagation delay by converting the ripple carry in such a way that the carry over a group of bits of the adder becomes 2-level logic.