The ratio of unshaded squares to shaded squares is 15:10. This means that for every 15 unshaded squares, there are 10 shaded squares. This can also be simplified to 3:2, which means that for every 3 unshaded squares, there are 2 shaded squares.
It is important to keep in mind that the ratio is not equal to the fraction, it's just a way to express the relationship between the two.