Which term is described as 'number to verify entry'?

• A. Parity check
• B. Check digit
• C. Echo check
• D. Error detection

Answer: (C)

A check digit is a digit added to a number specifically to verify entry. It’s calculated from the other digits using a rule (often involving modular arithmetic) so that when the full number is read or entered again, the check digit can be recomputed and compared. If the check digit matches, the entry is likely correct; if not, an error is detected. This is exactly what the phrase “number to verify entry” describes—the extra digit serves as a verification tool for the rest of the number.

Other terms describe different error-detection ideas: a parity check uses a separate parity bit to detect errors in a group of bits, not an appended digit; an echo check isn’t a standard, widely used term for verifying a numeric entry; and error detection is the broad concept encompassing many methods, not a single verifying digit. In real-world use, identifiers like ISBNs or credit card numbers rely on a check digit to validate the entire number.