Concrete pipe

The concrete pipe is cylindrical, with an inner diameter of 60 cm and an outer diameter of 67 cm. If it is 10 m long, calculate its surface.

Correct answer:

S =  40 m²

Step-by-step explanation:

$$\begin{gathered} d_1=60\text{cm}\to \text{m}=60:100\text{m}=0.6\text{m} \\ {d}_2=67\text{cm}\to \text{m}=67:100\text{m}=0.67\text{m} \\ L=10\text{m} \\ {r}_1=d_1/2=0.6/2=\frac{3}{10}=0.3\text{m} \\ {r}_2=d_2/2=0.67/2=\frac{67}{200}=0.335\text{m} \\ {S}_1=\pi \cdot L\cdot (d_1+d_2)=3.1416\cdot 10\cdot (0.6+0.67)\doteq 39.8982{\text{m}}^2 \\ {S}_2=2\cdot (\pi \cdot r_2^2-\pi \cdot r_1^2)=2\cdot (3.1416\cdot 0.335^2-3.1416\cdot 0.3^2)\doteq 0.1396{\text{m}}^2 \\ S=S_1+S_2=39.8982+0.1396=40{\text{m}}^2 \end{gathered}$$

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