SOLUTION: Find the thickness of the spherical shell. Two metal spheres of radii 8cm and 13cm , respectively are melted down and a cast into a hallow sphere of external radius 15cm.

Question 1189060: Find the thickness of the spherical shell. Two metal spheres of radii 8cm and 13cm , respectively are melted down and a cast into a hallow sphere of external radius 15cm.
Found 2 solutions by Boreal, ikleyn:
Answer by Boreal(15235)   (Show Source): You can put this solution on YOUR website!
The volume of the first is pi*8^3=512 π; the second is π*13^3=2197 π units cm^3.
The total volume is their sum or 2709 π cm^3.
The external radius of the resulting sphere has area 4πr^2 or 900 π cm^2, since r^2=225 cm^2
The thickness is the total volume of 2709π cm^3/900π cm^2
or 3.01 cm.
Answer by ikleyn(52781)   (Show Source): You can put this solution on YOUR website!
.
Find the thickness of the spherical shell. Two metal spheres of radii 8cm and 13cm ,
respectively are melted down and a cast into a HOLLOW sphere of external radius 15cm.
~~~~~~~~~~~~~~~~

            The solution by @boreal is incorrect: his calculations are WRONG.

            I came to bring a correct solution/answer.

The volume of the first sphere is = cm^3. the volume of the second sphere is = cm^3. The total metal volume is their sum or cm^3. We should find the radius "r" of the spherical hollow part from the equation - = . Cancel the common factors in all the terms of the equation. You will get then this equation - = 2709 = 3375 - 2709 = 666 r = = 8.733 cm (rounded). ANSWER. The thickness of the spherical shell is this difference 15 cm - 8.733 cm = 6.267 cm.

Solved (correctly).

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