There's 1 adult for every 10 students.
That means there's 1 adult, 1 student, and 9 students.
If there were 477 more students than adults at the last prom, the 477 more students comes from the 9 additional students (1 adult, 1 student, 9 students).
477 / 9 = 53
Starting with a ratio of 1 adult and 10 students, multiply both numbers by 53 giving us:
53 adults and 530 students
Check to make sure: 530 - 53 = 477. So there were 477 more students than adults last year.
Answer: 53 adults