The BBC website seems to say that Zimbabwe would qualify instead of Ireland, but surely if it was a tie, it would go down to net run rate between the two teams?
A BBC results table here indicates that Ireland has a superior net run rate to Zimbabwe and a tie would take them level on points.
This is explained by Cricinfo:
In that case, all three teams will be tied on five points each but both Afghanistan's and Ireland's net run rate will take a beating since the teams will be conceding as many runs as they score. While Afghanistan's NRR (0.34) is already below Zimbabwe's (0.42), Ireland's NRR (0.47) will slip below Zimbabwe's to a value of 0.377.
The point is that a tie does affect your net run rate in that it pulls in back towards zero. Consider a hypothetical example where a team has played one match, scored 200 in its 50 overs and conceded only 100. Their net run rate is now (200 - 100) / 50 = 2.00. Now add in a tie where both teams score 150 (doesn't actually matter what the score is): the net run rate is now ((200 + 150) - (100 + 150)) / 100 = 1.00; while the absolute difference in the number of runs has not changed (that's the definition of a tie!), the number of overs being considered has increased, so the net run rate always has a smaller magnitude after the tie than before.
As Cricinfo point out, the situation is different if the match is abandoned as that Ireland's run rate does not change.
