How to set different width for md-grid-tile

I use new Angular Material. This code produce grid with two columns:

<md-grid-list cols="2" rowHeight="10">
  <md-grid-tile></md-grid-tile>
  <md-grid-tile></md-grid-tile>
</md-grid-list>

How to set 20% width to first columns and remaning 80% to second?