Let the full cake represent,
[tex]c(1)=1[/tex]Therfore, the given problem is in the form of an arithmetic sequence,
[tex]1,\frac{2}{3},\ldots.[/tex]Here, n=5, d=-1/3, c(1)=1
[tex]c(5)=c(1)+(5-1)\times-\frac{1}{3}[/tex]Therefore,
[tex]\begin{gathered} c(5)=1-\frac{4}{3} \\ =-\frac{1}{3} \end{gathered}[/tex]So, the remaining amount of cake is -1/3.