Question 730238
You might be trying to ask a different question, that you are not adding "more" acid, but are adding WATER, which is actually a bad idea, depending on the acid.


Assuming that you are trying to ask the different question, about dilution,
Try to visualize with proportional thinking:


The acid is being diluted by (4/5), so it would become 80% acid.  


If you are in fact, asking the question word-for-word as written, then this would be a non-problem, in that you would just have 50 pints of 20% acid.