Answer
$\$0.8$
Work Step by Step
The variation model described by the problem is $
C=\dfrac{k}{n}
,$ where $C$ is the cost and $n$ is the number produced.
Substituting the known values in the variation model above results to
\begin{array}{l}\require{cancel}
1.20=\dfrac{k}{4000}
\\\\
k=1.2(4000)
\\\\
k=4800
.\end{array}
Therefore, the variation equation is
\begin{array}{l}\require{cancel}
C=\dfrac{4800}{n}
.\end{array}
Using the variation equation above, then
\begin{array}{l}\require{cancel}
C=\dfrac{4800}{6000}
\\\\
C=0.8
.\end{array}
Hence, the cost is $
\$0.8
$ per DVD.
