The volleyball ball

The volleyball ball can have a circumference after inflation of at least 650 max 750 mm. What volume of air can this ball hold, if its circumference is the average of the minimum and maximum inflation of the ball.

Correct answer:

V =  5.7922 l

Step-by-step explanation:

$$\begin{gathered} o_1=650\text{mm}\to \text{dm}=650:100\text{dm}=6.5\text{dm} \\ {o}_2=750\text{mm}\to \text{dm}=750:100\text{dm}=7.5\text{dm} \\ o=\frac{o_1+o_2}{2}=\frac{6.5+7.5}{2}=7\text{dm} \\ o=2\pi r \\ r=o/(2\pi )=7/(2\cdot 3.1416)\doteq 1.1141\text{dm} \\ V=\frac{4}{3}\cdot \pi \cdot r^3=\frac{4}{3}\cdot 3.1416\cdot 1.1141^3=5.7922\text{l} \end{gathered}$$

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