Excel: show raw value of two other cells?

I have an Excel table with three columns:

London     12     13
Paris      14     15

I want to add another column containing a string made up the value of column 2 and column 3 together, separated by a "/". Like this:

London     12     13    12/13
Paris      14     15    14/15

How do I do show the raw values, rather than calculating the fraction? If I put the formula =B2/C2 into D2 then unsurprisingly, I just get a fraction.