Question 1207242
.
A cylindrical can holds three tennis balls. each ball has a diameter of 6 cm, 
which is the same diameter as the cylinder, and the cylinder is filled to the 
top. Calculate the volume of space in the cylinder not taken up by the tennis 
balls. Round to the nearest cubic centimeter
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The formula in the post by @josgarithmetic for the empty volume


        {{{18*pi*(6/2)^2-(4/3)pi*(6/2)^2}}}  cubic centimeters


is  FATALLY  INCORRECT.  A correct formula is


        {{{18*pi*(6/2)^2-3*(4/3)pi*(6/2)^3}}}  cubic centimeters.


It gives the value of    {{{3.14159265*(18*(6/2)^2-3*(4/3)*(6/2)^3)}}} = 339.292  cm^3.


Notice that for the given configuration, the empty space is exactly half of the occupied space.


It was known just to  Archimedes about  2300  years ago,  when he discovered the formula for the volume of a sphere.