Pythagoras and the Ratios — Julie Ellis

Pythagoras and his cousin Octavius want to win a music contest but first they must figure out how to play their musical instruments in unison, something that's never been done before. Pythagoras makes an important discovery-notes that sound pleasant together have a certain mathematical ratio. When Pythagoras applies this ration to his cousin's pipes and lyres, the result is music to his ears.