Fractions ("X out of Y complete") in RTL Languages

We are working on RTL support in an application. One of the elements in our app is a progress bar that shows the number of slides of a deck that the users has completed, as well as a graphical expression of the overall proportion.

We are pretty sure (but not certain) based on other research that a progress bar in an RTL context should fill right to left. One thing we are not sure of, however, is how the concept of, say, "3 out of 5 slides complete" should be expressed in an RTL language.

Currently, we have "3 / 5" displayed on the progress bar, following the general advice that numbers should usually be displayed the same in RTL and LTR languages. But is that true for fractional quantities? Would this be properly written as "5 / 3" or even "5 \ 3"?

See the picture below. (I am aware that the forward and back images need to be switched for RTL as well; ignore that for the moment.)