Answer :
For this problem we use the formula for the area of an equilateral triangle
[tex]\begin{gathered} AT\text{ = }\frac{\sqrt[]{3}}{4}\cdot a^2\text{ = }\frac{\sqrt[]{3}}{4}(10in)^2\text{ = 25}\sqrt[]{3}in^2 \\ \end{gathered}[/tex]Then, the probability that the piece lands on the triangles is the area of the triangle over the area of the reactangle
[tex]P=\frac{AT}{AR}=\text{ }\frac{25\sqrt[]{3}in^2}{30\cdot20in^2}=\frac{\sqrt[]{3}}{24}[/tex]