[tex]min-minute;\ s-second\\\\1min=60s\\\\\begin{array}{ccc}40s&-&0.5\ DVD\\60s&-&x\ DVD\end{array}\ \ |cross\ multiply\\\\\\40\cdot x=60\cdot0.5\\40x=30\ \ \ \ |divide\ both\ sides\ by\ 40\\x=\frac{30}{40}\\\\x=\frac{3}{4}\ (DVD)\\\\\frac{3}{4}=0.75\\\\Answer:\boxed{0.75DVD\ per\ 1\ min}[/tex]
