well, a whole will be five fifths or 5/5.
now, he only plays 1/5 in 1/15, how many minutes will it take to play the whole 5/5 of the song?
[tex]\bf \begin{array}{ccll}
\stackrel{part}{song}&\stackrel{part}{minutes}\\
\text{\textemdash\textemdash\textemdash}&\text{\textemdash\textemdash\textemdash}\\
\frac{1}{5}&\frac{1}{15}\\\\
\frac{5}{5}&m
\end{array}\implies \cfrac{\frac{1}{5}}{\frac{5}{5}}=\cfrac{\frac{1}{15}}{m}\implies \cfrac{\frac{1}{5}}{\frac{5}{5}}=\cfrac{\frac{1}{15}}{\frac{m}{1}}\implies \cfrac{1}{5}\cdot \cfrac{5}{5}=\cfrac{1}{15}\cdot \cfrac{1}{m}[/tex]
[tex]\bf \cfrac{1}{5}=\cfrac{1}{15m}\implies 15m=5\implies m=\cfrac{5}{15}\implies m=\stackrel{\textit{minutes}}{\cfrac{1}{3}}[/tex]
