Fractions can’t be used for measured numbers (or the manipulation of measured numbers). The reason is that you can’t show sig figs with fractions. For instance 22/7 is the fraction for pi which has an infinite number of digits. Obviously, no instrument is that accurate, so you have to “round and truncate” pi to show the proper number of sig figs. We’ll talk about sig figs more later. This is good enough for this first introduction.