Format values in text cell
Using extra cells (which can be hidden) appears to be the only way I have found to control the Automatic formatting that Numbers applies.

In separate cells for each desired number, do the calculation.
A2*60 then in another cell, B2*60

In your Range column, concatenate the results.  So if the cells containing 20 and 30 are in E2 and F2 then Range would have this formula:

E2 &amp; " - " &amp; F2

or:

concatenate(E2," - ",F2)

Then if desired, hide E and F columns.