Question 26064
#1. Follow the acid.
Start with 80%(5)
Add 2%(x);  x because the amount of fluid added is unknown
End up with: 10%(5+x)
EQUATION:
  80%(5)+2%(x)=10%(5+x)
Multiply through by 100 to get:
  80(5)+2x=10(5+x)
  400+2x=50+10x
     8x=350
      x= 43.75ml (amount of 2% fluid you need to add)

Cheers,
Stan H.