Answer to Question #238253 in Statistics and Probability for Paul

Question

 set of 1000 data items is stored redundantly in a database with 3 copies existing (therefore there are 3000 entries in the database). During a break-in, 100 random data entries are maliciously modified by inverting the letters and numbers. What is the likelihood that the retrieval attempts for the first 50 data items (each retrieval attempt retrieving all copies of a data item) result in three uncorrupted data copies (i.e. in the situation where all three copies have not been modified) ? What is the likelihood that the same retrieval attempt for 50 items results in all items being correctly restored by a majority vote (i.e. two of the three copies have not been tampered with)?