Answer :
Answer: Each will get 1/15 of the original size of the cake
[tex]\begin{gathered} \text{Let the original size of the cake be x} \\ \text{She has }\frac{1}{5}\text{ of the cake left after the party} \\ \text{The remaining cake left is }\frac{1}{5}\text{ x original size of the cake} \\ =\text{ }\frac{1}{5}\cdot\text{ x} \\ =\text{ }\frac{x}{5} \\ \text{She divide the cake among her mum, dad, and brother equally} \\ \frac{x}{5}\text{ divided by 3} \\ \frac{x}{5}\cdot\text{ }\frac{1}{3} \\ =\text{ }\frac{x}{15} \\ \text{Each will get }\frac{1}{15\text{ }}\text{ of the original size of the cake} \end{gathered}[/tex]