Geometric Solid

A concrete pipe is 1.0 m long. The inside and outside diameters are 60 cm and 75 cm, respectively.

What is the volume of the concrete (in cubic meters) needed to make 25 pieces of pipe?

Correct answer:

V =  3.98 m³

Step-by-step explanation:

$$\begin{gathered} L=1.0\text{m} \\ d=60\text{cm}\to \text{m}=60:100\text{m}=0.6\text{m} \\ D=75\text{cm}\to \text{m}=75:100\text{m}=0.75\text{m} \\ n=25 \\ {S}_1=\pi \cdot (D/2{)}^2=3.1416\cdot (0.75/2{)}^2\doteq 0.4418{\text{m}}^2 \\ {S}_2=\pi \cdot (d/2{)}^2=3.1416\cdot (0.6/2{)}^2\doteq 0.2827{\text{m}}^2 \\ S=S_1-S_2=0.4418-0.2827\doteq 0.159{\text{m}}^2 \\ {V}_1=S\cdot L=0.159\cdot 1\doteq 0.159{\text{m}}^3 \\ V=n\cdot V_1=25\cdot 0.159=3.98{\text{m}}^3 \end{gathered}$$

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