For the full exchange rate between 1% TA and 5% DA:
1 + 2*TA% + 2% + DA% - DA%*TA% - 1%*DA% = 1 + 2*TA% + DA% - DA%*TA% - 5%*TA% + 5%
5%*TA% = 1%*DA% + 3%
multiply by 100 for simplicity
5*TA% = DA% + 3
5*60% = DA% + 3
3 - 3 = 0% DA (okay, this checks out with our earlier simplified example)
5*TA% = 20% + 3
TA% = 64% (so it turns out that having more DA actually slightly devalues TA because additional TA detracts from DA)
Regardless, not going to hit that 1% TA / 5% DA tradeoff point any time soon.
TAb+TA% = DAb*DA% + 100*(DAb - TAb*2)