What is the main idea of the passage?

Error correction adds structured check information so a receiver can detect and sometimes repair damaged data within defined limits. (The passage explains structured redundancy, gives an example, then emphasizes capacity costs and correction limits.)

Why can the receiver identify the likely error in 101?

Two matching bits provide evidence that the different middle bit was changed. (Under the stated three-copy method, the majority matches the sent value and isolates the lone disagreement.)

What does “redundancy” mean here?

extra structured information added to protect the original data (The second paragraph defines redundancy as calculated check information added beyond the original data.)

What tradeoff comes with adding more protection?

It uses additional storage or transmission capacity. (The fourth paragraph directly states the capacity cost of stronger protection.)

The Quiet Work of Error Correction: Level 4 Reading Comprehension Questions

A message crossing a noisy channel can change before it arrives. A radio signal may encounter interference, or a bit stored on a device may flip. Simply sending the original data gives the receiver no independent way to decide whether every symbol survived correctly.

Error-correcting systems add carefully designed redundancy. This is not random repetition. Extra check information is calculated from the original data so that valid messages follow a known structure. If a received pattern breaks that structure, the receiver can detect an error. With enough check information, it may also infer which part changed and repair it.

A simple illustration uses three copies of one bit. If 1 is sent as 111 but arrives as 101, majority voting suggests that the middle bit flipped. The method is wasteful, since it triples the data, and it cannot handle every pattern of damage. Practical codes use more efficient mathematical relationships among many bits.

Correction always has limits. A code designed to repair one changed bit may only detect a larger cluster, and severe damage can overwhelm it. More protection also consumes storage or transmission capacity. Engineers therefore match a code to expected noise and acceptable cost. The receiver's repair may look effortless, but it depends on information deliberately added before trouble occurred. Redundancy gives the message enough structure to reveal some of its own injuries.

Comprehension questions