Question

A solution contains $75$ mg of $NaCl$ per mL. To what extent must it be diluted to give a solution of concentration $15$ mg of $NaCl$ per mL of solution?

Answer 1

Let C and V be the initial concentration and initial volume respectively.
Let C' and V' be the final concentration and final volume respectively.
$CV=C^{\prime }{V}^{\prime }$
$75mg/ml\times V=15mg/mL\times V^{\prime }$
$V^{\prime }=5V$
Hence, the final volume should be five tines the original volume.