You get about AR$0.2 per US$1 less. That is hardly "20%".
So if you got AR$9.7 to US$1 on Friday, then you might have only gotten AR$9.5 to US$1 with US$20s.
0.2 / 9.7 = 2.06% less
"20% Less" = AR$7.76
That's a pretty big difference. But then again, if you are willing to take AR$155.20 for each of your US$20s (AR$7.76 per US$1), I'll gladly take all of them off of your hands.