Summary: This article discusses a relatively unnoticed application of mathematics by describing its connection with an aspect of music, in particular, the musical scales. Stemming from a problem found in a Year 9 mathematics textbook commonly used in Singapore, the article illustrates the role of mathematics in musical scales by first considering the frequency ratios of consecutive musical notes in the ‘just scale’ and secondly explaining how an anomaly in the ‘just scale’ caused by the uneven frequency ratios is resolved with the help of mathematics, thereby leading to the development of the well-tempered scale. The article ends with an exploration of the frequency ratios of consecutive musical notes in the well-tempered scale. Not only does the article aim to broaden the teachers’ horizons with such an introduction to the mathematical aspect of music, it also hopes to enrich their mathematical experiences as well.