Teenagers’ use of emoticons in school writing. Due to the popularity of instant messaging and social networking, informal elements such as emoticons (e.g., the symbol “:)”

to represent a smile) and abbreviations (e.g., “LOL” for

“laughing out loud”) have worked their way into teenagers’

school writing assignments. A Pew Internet and American Life Project (Apr. 2008) survey interviewed 700 randomly selected U.S. teenagers by telephone on their writing habits. Overall, 448 of the teenagers admitted using at least one informal element in school writing assignments.

Based on the survey results, construct a 99%

confidence interval for the proportion of all U.S. teenagers who have used at least one informal element in school writing assignments. Give a practical interpretation of the interval.