A work sampling study was performed on the day-shift maintenance department in a power generating station. The day-shift consists of four repair persons, each of whom works independently to repair equipment when it breaks down. A total of 900 observations for all workers were taken during a fourweek period (160 total hours of station operation). The observations were classified into one of the following categories: (1) maintenance person repairing equipment, or (2) maintenance person idle. There were a total of 454 observations in category 1. It is known that 83 equipment repairs were made during the 4 weeks. How many more observations would be required to be 90% confident that the true proportion of category 1 activity is within 4% of the true proportion indicated by the observations?