To what volume must 1580mL of 0.2005 N solution be diluted so that the resulting solution will be 0.1899 M? How much water will be needed in the dilution?
you want to reduce the concentration by a factor of .1899/.2005 = 0.9471
So, the volume must increase by that factor, to 1580/.9471 = 1668 mL.
Just subtract to figure the amount of water added.