now, a whole in sevenths, will just be 7/7.
now, we know the pump can do 4/7 of the tank in 20 minutes, how many minutes will it take to do 7/7, or the whole tank?
[tex]\bf \begin{array}{ccll}
\stackrel{part}{tank}&minutes\\
\text{\textemdash\textemdash\textemdash}&\text{\textemdash\textemdash\textemdash}\\
\frac{4}{7}&20\\\\
\frac{7}{7}&m
\end{array}\implies \cfrac{\quad \frac{4}{7}\quad }{\frac{7}{7}}=\cfrac{20}{m}\implies \cfrac{4}{7}\cdot \cfrac{7}{7}=\cfrac{20}{m}\implies \cfrac{4}{7}=\cfrac{20}{m}
\\\\\\
4m=140\implies m=\cfrac{140}{4}\implies m=35[/tex]
