Question 1085115
Volume of barrel is pi*r^2*h=25*pi*15=375 pi in^3
volume of hemisphere is (2/3)*pi*r^3=(250/3)*pi in^3
divide the first by the second, and pi cancels
375/(250/3)=375*3/250=1125/250
needs five trips
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Check using the fact that 1 1/2 spheres or 3 hemispheres will fit into the barrel physically.  That would be the minimum, but there is empty space, and that would require four full hemispheres and part of a fifth.