Geometric Solid

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

What is the volume of 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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