Expand a div to fill the remaining width

Question

I want a two-column div layout, where each one can have variable width e.g.

Answer 1

If the width of the other column is fixed, how about using the calc CSS function working for all common browsers:

width: calc(100% - 20px) /* 20px being the first column's width */

This way the width of the second row will be calculated (i.e. remaining width) and applied responsively.