The quinceañera (the young woman being celebrated) dances the first part of the waltz first with her father, for
about 60 seconds.
She then dances with her padrino (godfather), for about
20 seconds.
She then dances with each of the chambelanes, the
young men she has chosen to accompany her on her
special day, for about 15 seconds each.
Bárbara's quinceañera is coming up, and she has to
choose a song that will be exactly the right length, so that
she is not stuck dancing by herself at the end of the song.
How long should her song be? Show your thinking
mathematically.