We know: 1/4 of Ms. Sing's student chose guitar, with a total of 24 students in the class. Doing mental math, we should be able to realize that 1/4 of 24 is 6, because if you divide 24 by 4 you get 6.
6 of her students play guitar.
We needed to find what fraction of Ms. Sing's class as a whole number plays the guitar.