This is a question from computer networks paper to calculate number of errors can be detected in a word using even parity bit

Question

Question

A communication system uses even parity and adds a parity bit to each seven bit. Thus a word(8mbits) transmitted consists of 7 data bits and one parity bit. How many errors can it detect in a word?

Answer 1

The main purpose of adding Parity bits is to detect single bit errors.

When a single bit is transmitted incorrectly, the resulting parity changes from even to odd. Thus, the error becomes visible.

Apart from that, multiple bit errors can be detected, when they also change the resulting parity. For seven data bits, this is the case for 1, 3, 5 or 7 incorrect bits. On the contrary, 2, 4, and 6 erroneous bits cannot be detected, as they leave the parity unchanged.