We are given a right prism whose bases are congruent regular pentagons. The side length of each pentagon is approximately $10.2$ mm, and the apothem measures $7$ mm. The height of the prism is $4$ mm. We need to find the volume of the prism, rounding to the nearest tenth.

GeometryPrismVolumePentagonArea3D Geometry
2025/4/14

1. Problem Description

We are given a right prism whose bases are congruent regular pentagons. The side length of each pentagon is approximately 10.210.2 mm, and the apothem measures 77 mm. The height of the prism is 44 mm. We need to find the volume of the prism, rounding to the nearest tenth.

2. Solution Steps

The volume VV of a prism is given by the formula
V=AbasehV = A_{base} \cdot h,
where AbaseA_{base} is the area of the base and hh is the height of the prism.
The area of a regular polygon with nn sides is given by
A=12aPA = \frac{1}{2} \cdot a \cdot P,
where aa is the apothem and PP is the perimeter.
In our case, the base is a regular pentagon, so n=5n=5.
The side length is 10.210.2 mm, so the perimeter is P=510.2=51P = 5 \cdot 10.2 = 51 mm.
The apothem is a=7a = 7 mm.
So the area of the pentagon base is
Abase=12751=3572=178.5A_{base} = \frac{1}{2} \cdot 7 \cdot 51 = \frac{357}{2} = 178.5 mm2^2.
The height of the prism is h=4h = 4 mm.
So the volume of the prism is
V=Abaseh=178.54=714V = A_{base} \cdot h = 178.5 \cdot 4 = 714 mm3^3.

3. Final Answer

The volume of the prism is 714.0714.0 mm3^3.

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