Question 1205012
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Two circular metal {{{highlight(cross(disc))}}} <U>disks</U> of radii 3.3cm and 5.6cm are melted down and cast 
into a single circular disc of the same thickness. Find the radius of this disc.
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<pre>
Equate the volumes

    {{{pi*3.3^2*h}}} + {{{pi*5.6^2*h}}} = {{{pi*r^2*h}}}.


where "h" is the common thickness.  

Cancel common factor  {{{pi*h}}}.  Get

    {{{3.3^2 + 5.6^2}}} = {{{r^2}}}

    42.25 = {{{r^2}}}

    r = {{{sqrt(42.25)}}} = 6.5 cm.


<U>ANSWER</U>.  The radius of the resulting disk is 6.5 cm.
</pre>

Solved.


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The lesson to learn from this my solution is the Law of mass conservation.