Question 1172961
He MUST add the acid TO the water, for safety.



Strictly in volumes,  4+3 parts is 7 parts of volume.  This is 4 parts of the concentrated HCl to 7 part of finished mixture.  Or,  3 parts of water to 7 parts of finished mixture.



Or, just as the given ratio,  4 parts conc. acid to 3 parts water.

{{{3/4=Q/20}}}


{{{Q=3*5}}}


{{{highlight(Q=15)}}}------------liters of water