The following diagram shows equilateral triangle $\vartriangle ABC$ and three other triangles congruent to it. The other three triangles are obtained by sliding copies of $\vartriangle  ABC$ a distance $\frac18 AB$ along a side of $\vartriangle ABC$ in the directions from $A$ to $B$, from $B$ to $C$, and from $C$ to $A$. The shaded region inside all four of the triangles has area $300$. Find the area of $\vartriangle ABC$.
[img]https://cdn.artofproblemsolving.com/attachments/3/a/8d724563c7411547d3161076015b247e882122.png[/img]
1. **Understanding the Problem:**
   We are given an equilateral triangle $\triangle ABC$ and three other triangles congruent to it. These triangles are obtained by sliding copies of $\triangle ABC$ a distance $\frac{1}{8} AB$ along a side of $\triangle ABC$ in the directions from $A$ to $B$, from $B$ to $C$, and from $C$ to $A$. The shaded region inside all four of the triangles has an area of $300$. We need to find the area of $\triangle ABC$.

2. **Analyzing the Shaded Region:**
   The shaded region is formed by the intersection of the four congruent triangles. To find the area of $\triangle ABC$, we need to determine what fraction of $\triangle ABC$ the shaded region represents.

3. **Identifying the Diamonds:**
   By sliding the triangles, we form diamond shapes at the corners of $\triangle ABC$. Each diamond has angles $60^\circ, 120^\circ, 60^\circ, 120^\circ$. 

4. **Calculating the Area of the Diamonds:**
   Each diamond is formed by sliding a triangle a distance $\frac{1}{8} AB$. The area of each diamond can be calculated by considering the proportion of the area of $\triangle ABC$ it occupies. Since the diamonds are formed by sliding the triangles, each diamond takes up $\frac{2}{64}$ of the area of $\triangle ABC$.

5. **Calculating the Area of the Long Strip:**
   The long strip between two diamonds also needs to be considered. This strip, along with two diamonds, makes up $\frac{15}{64}$ of the area of $\triangle ABC$ through length ratios.

6. **Total Shaded Area:**
   The total shaded area is the sum of the areas of the diamonds and the long strip. This is given as $\frac{25}{64}$ of the area of $\triangle ABC$.

7. **Setting Up the Equation:**
   Given that the shaded area is $300$, we can set up the equation:
   \[
   \frac{25}{64} \times \text{Area of } \triangle ABC = 300
   \]

8. **Solving for the Area of $\triangle ABC$:**
   \[
   \text{Area of } \triangle ABC = 300 \times \frac{64}{25}
   \]
   \[
   \text{Area of } \triangle ABC = 300 \times 2.56
   \]
   \[
   \text{Area of } \triangle ABC = 768
   \]

The final answer is $\boxed{768}$.