If you get to pick a shape of a 20 mile perimiter what shape would be most efficient and why

The shape's efficiency is determined by what you define efficency as: If you were trying to enclose the maximum area, a circle. If you were trying to plow with a tractor, a long rectangle. If you were irrigating with a sprinkler, a circle.
So decide what you mean by efficiency.

If you were using the perimeter material to enclose the maximum area, a circle would be your choice.

If you were trying to enclose the maximum rectangular area, a square would be your choice.

i would pick a square because it is a simple shape

To understand why a circle is the most efficient shape for enclosing the maximum area with a given perimeter, let's break it down step by step:

1. Start with the basic formula for calculating the perimeter of a shape: Perimeter = 2πr, where r is the radius of the shape.

2. To find the maximum area enclosed by a shape with a fixed perimeter, we need to find the shape that maximizes the value of the area formula.

3. The formula for the area of a circle is A = πr^2, where A is the area and r is the radius.

4. Since we have a fixed perimeter, we can express r in terms of the perimeter using the perimeter formula: r = perimeter / (2π).

5. Substituting this value of r into the area formula, we get A = π * (perimeter / (2π))^2.

6. Simplifying this equation, we get A = (perimeter^2) / (4π).

7. Now, let's compare this with the formulas for other shapes. For a square, the perimeter formula is P = 4s, where s is the length of each side. So, the side length of a square given a fixed perimeter would be s = perimeter / 4. The area of the square would then be A = s^2 = (perimeter / 4)^2 = (perimeter^2) / 16.

8. Comparing the area formulas, we can see that the area of a circle (A = (perimeter^2) / (4π)) is larger than the area of a square (A = (perimeter^2) / 16) for the same fixed perimeter.

9. This means that a circle is the most efficient shape for enclosing the maximum area with a given perimeter.

However, it's important to note that the concept of efficiency can vary depending on the specific context or purpose. For example, if you were considering factors like ease of construction, cost, or usability for specific tasks, other shapes like rectangles or squares might be more efficient.