Game of Fusions
A solid ball is prepared after melting 10 smaller balls. The external diameter of each small ball is 10 mm. What is the radius of the big ball, if 5 out of the small balls had a thickness of 1 mm and the remaining 5 were solid metal? Also, what would be the thickness of a hollow ball prepared by melting the big ball and making a bigger hollow ball of 40 mm diameter?